Jackie

Jackie Lau, Senior Tooling Engineer and Expert of plastic injection molding, experienced in plastic injection molding and tooling for more than 15 years. The founder and Director of Eco Molding & Sositar Mould.

A Comparison of the HDPE, LDPE and LLDPE Resins

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HDPE,LDPE,LLDPE injection molding

This article is to analyze the engineering application scope, the respective characteristics of their applications and the application scope of HDPE, LDPE and LLDPE resin materials from  the aspects of raw material, molecular structure, density, crystallinity, softening point, corrosion resistance, temperature range, mechanical properties, tensile strength, elongation at break, resistance to environmental stress cracking, industrial production principles, processes and additives, etc.

As one of the five commonly used synthetic resins, polyethylene is a synthetic resin that boasts the largest production capacity and the highest import volume in China. At present, China is already the largest importer and the second largest consumer of polyethylene in the whole world. Polyethylene is a mixture of ethylene monomers, while polyethylene plastic is a plastic product made with polyethylene resin as the base material, combined with a small dose of additives, such as antioxidants and slip agents. Polyethylene is mainly divided into three categories: linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and high-density polyethylene (HDPE).

1 . High-density polyethylene, abbreviated as HDPE

HDPE is non-toxic, tasteless and odorless, with a density of 0.940 to 0.976 g/cm3. It is produced through low-pressure polymerization with the help of the Ziegler catalyst, so high-density polyethylene is also referred to as low-pressure polyethylene.

HDPE is a thermoplastic resin, which is copolymerized with ethylene to form the high crystallinity and non-polarity properties. The original HDPE has a milky white appearance and a somewhat semi-transparent state in the thin section. It is excellent in resistance to most household and industrial chemicals, able to resist corrosion and dissolution by strong oxidizing agents (concentrated nitric acid), as well as acid / alkali / salt and organic solvents (carbon tetrachloride). The polymer is non-hygroscopic and features a great resistance to water vapor and can be used for moisture-proof and anti-permeability purposes.

Its weakness is that its resistance to aging and environmental stress cracking is not as good as that of LDPE. Especially, its performance will be lowered under the effect of thermal oxidation, so when made into plastic coils, high-density polyethylene is often added with anti-oxidants and UV absorbers to improve the weakness.

2 . Low density polyethylene, abbreviated as LDPE

LDPE is non-toxic, tasteless and odorless, with a density of 0.910 to 0.940 g/cm3. It is produced through polymerization under the 100 to 300MPa high-pressure conditions, by using oxygen or an organic peroxide as the catalyst, so it is also referred to as high-pressure polyethylene.

Low-density polyethylene is the lightest variant among all polyethylene resins. Compared with high-density polyethylene, its crystallinity (55%-65%) and softening point (90-100°C) are relatively lower; it boasts great softness, extensibility, transparency, cold resistance and processability; with an outstanding chemical stability, it is resistant to acid, alkali and salt solutions. Its characteristics also include great electrical insulation and air permeability; low water absorption; and easy combustibility. It is soft in nature and features good elongation, electrical insulation, chemical stability, processability and resistance to low temperature (up to -70°C).

Its weaknesses are its deficiency in mechanical strength, moisture resistance, air permeability and resistance to solvents. The molecular structure is not regular enough, while its crystallinity (55% to 65%) and crystalline melting point (108 to 126°C) is also relatively lower.

Its mechanical strength is lower than that of high-density polyethylene, and its anti-seepage coefficient, thermal resistance and resistance to aging caused by sun exposure are also rather poor. Under sunlight or high temperature conditions, it is prone to aging and discoloration, resulting in performance deterioration, so when made into plastic coils, low-density polyethylene is often added with anti-oxidants and UV absorbers to improve the weaknesses.

3 . Linear Low-density polyethylene, abbreviated as LLDPE

LLDPE is non-toxic, tasteless and odorless, with a density between 0.915 and 0.935 g/cm3. It is a copolymer produced through high-pressure or low-pressure polymerization, using ethylene and a small dose of high-grade α-olefins (such as 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, etc.) as the catalysts. The molecular structure of conventional LLDPE is characterized by its linear backbone, with few or no long chain branches, but containing some short chain branches. Without long chain branches, the polymer is endowed with a higher crystallinity.

Compared with LDPE, LLDPE boasts the advantages of higher strength, greater toughness, stronger rigidity, as well as better resistance to heat and cold. In addition, it also features outstanding resistance to environmental stress cracking and tear strength, while being resistant to acids, alkalis and organic solvents.

To sum up, the three above-mention materials play an important role in different types of anti-seepage projects. HDPE, LDPE and LLDPE all boast excellent insulation, moisture resistance and impermeability, and are non-toxic, tasteless and odorless, allowing them to be extremely widely applied in agriculture, aquaculture, artificial lakes, reservoirs and rivers. Therefore, they are vigorously promoted and popularized by the Bureau of Fisheries of the Ministry of Agriculture, the Shanghai Fisheries Research Institute, and the Fishery Machinery and Instrument Research Institute.

In the strong acidic, strong alkaline, strong oxidative and organic solvent environments, the properties of HDPE and LLDPE can be made full use of. Especially, in terms of resistance to strong acid, strong alkali, strong oxidation and organic solvents, HDPE performs far better than the other two materials, so the anti-seepage and anti-corrosion coil materials made from HDPE are widely used in the chemical and environmental protection industries.

Low-density polyethylene also features great resistance to acids, alkalis, and salt solutions, as well as outstanding elongation, electrical insulation, chemical stability, processability, and resistance to low temperature. Therefore, it is widely used in agriculture, aquaculture, packaging (especially low-temperature packaging) and the cable industry.

A Comparison of the Properties of HDPE, LDPE and LLDPE

Plastic Name High-Density Polyethylene Low-Density Polyethylene Linear Low-Density Polyethylene
Property Comparison HDPE LDPE LLDPE
Smell & Toxicity Nontoxic, tasteless and odorless Nontoxic, tasteless and odorless Nontoxic, tasteless and odorless
Density 0.940-0.976g/cm3 0.910-0.940g/cm3  0.915-0.935g/cm3
Crystallinity 85-65% 45-65% 55-65%
Molecular Structure Contains only carbon-carbon and carbon-hydrogen bonds, requiring more energy to break The polymer has a small molecular weight and can be broken with less energy Linear structure with few branch and short chains, can be broken with less energy
Softening Point 125-135℃ 90-100℃ 94-108℃
Mechanical Properties High strength, toughness and rigidity Low mechanical strength High strength, toughness and rigidity
Tensile Strength High Low Higher
Elongation at Break Higher Low High
Impact Strength Higher Low High
Resistance to Moist & Water Good permeability to water, vapor and air; low water absorption; great resistance to seepage Poor airproof and moisture-proof properties Good permeability to water, vapor and air; low water absorption; great resistance to seepage
Resistance to Acid, Alkali, Corrosion and Organic Solvents Resistant to strong oxidants, acids, alkalis and various salts; insoluble in any organic solvents. Resistant to acid, alkali and salt solutions, but with poor resistance to solvents Resistant to acids, alkalis, and organic solvents
Resistance to Heat / Cold Great resistance to heat and cold, even so in the temperature range from room temperature to as low as -40°C; excellent impact resistance; embrittlement temperature < -90°C Low resistance to heat; embrittlement temperature <-70°C Great resistance to heat and cold; embrittlement temperature <-90°C
Resistance to Environmental Stress Cracking Good Better Good

Sink Marks Injection Molding Defects

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The dents and hollows on the surface of a plastic product are referred to as “sink marks”. In addition to the appearance of the product, sink marks also affect the quality and strength of the final product. The reasons for sink marks are related to molding processing, mold design and the choice of the plastic material.

sink marks plastic injection molding defects

Raw Material

The shrinkage rates of different plastic materials are different. Usually, the raw materials that are prone to sink marks are crystalline, such as nylon. During the injection molding process, the crystalline plastic is heated to a fluid state, with the molecules randomly arranged; when filled into the cold cavity, the plastic molecules are slowly arranged neatly to crystallize. As a result, the volume is shrunk to be smaller than the specified dimensional range, which is referred to as the “sink mark”.

The shrinkage rates of various plastic materials(mold shrinkage rate) are shown below:

Name of the polymer Explicit name of the polymer Min Value(%) Max Value(%)
ABS Acrylonitrile-Butadiene Styrene 0.7 1.6
ABS FR Acrylonitrile-Butadiene Styrene flame retardant 0.3 0.8
ABS High Heat Acrylonitrile-Butadiene Styrene High Heat 0.4 0.9
ABS High Impact Acrylonitrile-Butadiene Styrene High Impact 0.4 0.9
ABS/PC Acrylonitrile-Butadiene Styrene/Polycarbonate 0.5 0.7
ABS/PC 20% GF Acrylonitrile-Butadiene Styrene/Polycarbonate 20% glass fiber 0.2 0.3
ABS/PC FR Acrylonitrile-Butadiene Styrene/Polycarbonate flame retardant 0.3 0.6
ASA Acrylonitrile Styrene Acrylate 0.4 0.7
ASA/PC Acrylonitrile Styrene Acrylate/Polycarbonate 0.3 0.7
ASA/PC FR Acrylonitrile Styrene Acrylate/Polycarbonate flame retardant 0.4 0.8
ASA/PVC Acrylonitrile Styrene Acrylate/Polyvinyl Chloride 0.3 0.7
CA – Cellulose Acetate Cellulose Acetate 0.3 1
CPVC – Chlorinated Polyvinyl Chloride CPVC – Chlorinated Polyvinyl Chloride 0.3 0.7
EVA Ethylene Vinyl Acetate 0.4 3.5
HDPE – High Density Polyethylene HDPE – High Density Polyethylene 1.5 4
HIPS – High Impact Polystyrene HIPS – High Impact Polystyrene 0.2 0.8
HIPS FR V0 High Impact Polystyrene flame retardant V0 0.3 0.6
LDPE – Low Density Polyethylene LDPE – Low Density Polyethylene 2 4
LLDPE – Linear Low Density Polyethylene LLDPE – Linear Low Density Polyethylene 2 2.5
PA 11 30% Glass fiber reinforced Polyamide 11 30% Glass fiber reinforced 0.5 0.5
PA 11 conductive Polyamide 11 conductive 0.7 2
PA 11 flexible Polyamide 11 flexible 1.4 1.8
PA 11 rigid Polyamide 11 rigid 0.7 2
PA 12 conductive Polyamide 12 conductive 0.7 2
PA 12 fiber reinforced Polyamide 12 fiber reinforced 0.7 2
PA 12 flexible Polyamide 12 flexible 0.7 2
PA 12 glass filled Polyamide 12 glass filled 0.7 2
PA 12 rigid Polyamide 12 rigid 0.7 2
PA 46 Polyamide 46 1.5 2
PA 46 30% GF Polyamide 46 30% glass fiber 0.3 1.3
PA 6 Polyamide 6 0.5 1.5
PA 6-10 Polyamide 6-10 1 1.3
PA 66 Polyamide 6-6 0.7 3
PA 66 30% GF Polyamide 6-6 30% glass fiber 0.5 0.5
PA 66 30% mineral filled Polyamide 6-6 30% mineral filled 0.6 1
PA 66 IM 15-30% GF Polyamide 6-6 impact modified 15-30% glass fiber 0.2 0.6
PA 66 impact modified Polyamide 6-6 impact modified 1.2 3
PBT Polybutylene Terephthalate 0.5 2.2
PBT 30% GF Polybutylene Terephthalate 30% glass fiber 0.2 1
PC 20-40% GF Polycarbonate 20-40% glass fiber 0.1 0.5
PC 20-40% GF FR Polycarbonate 20-40% glass fiber flame retardant 0.1 0.5
PC high heat Polycarbonate high heat 0.7 1
PC/PBT Polycarbonate/Polybutylene Terephthalate blend 0.6 1.1
PCTFE Polymonochlorotrifluoroethylene 0.5 1.5
PE 30% GF Polyethylene 30% glass fiber 0.2 0.6
PEEK Polyetheretherketone 1.2 1.5
PEEK 30% CF Polyetheretherketone 30% carbon fiber 0 0.5
PEEK 30% GF Polyetheretherketone 30% glass fiber 0.4 0.8
PEI Polyetherimide 0.7 0.8
PEI 30% GF Polyetherimide 30% glass fiber 0.2 0.4
PEI mineral filled Polyetherimide mineral filled 0.5 0.7
PEEK– Low cristallinity grade Polyetherketoneketone– Low cristallinity grade 0.004 0.005
PESU Polyethersulfone 0.6 0.7
PESU 10-30% GF Polyethersulfone 10-30% glass fiber 0.2 0.3
PET Polyethylene Terephtalate 0.2 3
PET 30% GF Polyethylene Terephtalate 30% glass fiber 0.2 1
PET 30/35% GF Impact modified Polyethylene Terephtalate 30/35% glass fiber impact modified 0.2 0.9
PET G Polyethylene Terephtalate Glycol 0.2 1
PE-UHMW Polyethylene -Ultra High Molecular Weight 4 4
PMMA Polymethylmethacrylate (Acrylic) 0.2 0.8
PMMA high heat Polymethylmethacrylate (Acrylic) high heat 0.2 0.8
PMMA Impact modified Polymethylmethacrylate (Acrylic) impact modified 0.2 0.8
Polyamide 66 (Nylon 66)/Carbon Fiber, Long, 30 % Filler by Weight Polyamide 66 (Nylon 66)/Carbon Fiber, Long, 30 % Filler by Weight 0.3 0.3
POM Polyoxymethylene (acetal) 1.8 2.5
POM impact modified Polyoxymethylene (acetal) impact modified 1 2.5
POM low friction Polyoxymethylene (acetal) low friction 1.8 3
POM mineral filled Polyoxymethylene (acetal) mineral filled 1.5 2
PP 10-20% GF Polypropylene 10-20% glass fiber 0.3 1
PP 10-40% mineral filled Polypropylene 10-40% mineral filled 0.6 1.4
PP 10-40% TALC Polypropylene 10-40% talc 0.9 1.4
PP 30-40% GF Polypropylene 30-40% glass fiber 0.1 1
PP copo Polypropylene copolymer 2 3
PP homo Polypropylene homopolymer 1 3
PP impact modified Polypropylene impact modified 2 3
PPA Polyphthalamide 1.5 2.2
PPA – 30% mineral Polyphthalamide– 30% mineral 1 1.2
PPA – 33% glass fiber Polyphthalamide – 33% glass fiber 0.5 0.7
PPA – 33% glass fiber – high flow Polyphthalamide– 33% glass fiber – high flow 0.74 0.76
PPA – 45% glass fiber Polyphthalamide– 45% glass fiber 0.1 0.3
PPE Polyphenylene Ether 0.5 0.8
PPE 30% GF Polyphenylene Ether 30% glass fiber 0.1 0.4
PPE FR Polyphenylene Ether flame retardant 0.6 1
PPE impact modified Polyphenylene Ether impact modified 0.6 1
PPE mineral filled Polyphenylene Ether mineral filled 0.3 0.7
PPS Polyphenylene Sulfide 0.6 1.4
PPS 20-30% GF Polyphenylene Sulfide 20-30% glass fiber 0.2 0.5
PPS 40% GF Polyphenylene Sulfide 40% glass fiber 0.2 0.5
PPS conductive Polyphenylene Sulfide conductive 0.3 1
PPS GF & mineral Polyphenylene Sulfide glass fiber & mineral 0.3 0.7
PS 30 % GF Polystyrene 30% glass fiber 0.2 0.2
PS crystal Polystyrene crystal 0.1 0.7
PS high heat Polystyrene high heat 0.2 0.7
PSU Polysulfone 0.7 0.7
PSU 30% GF Polysulfone 30% glass fiber 0.1 0.6
PSU mineral filled Polysulfone mineral filled 0.4 0.5
PVC 20% GF Polyvinyl Chloride 20% glass fiber 0.1 0.2
PVC plasticized Polyvinyl Chloride plasticized 0.2 4
PVC plasticized filled Polyvinyl Chloride plasticized filled 0.8 5
PVC rigid Polyvinyl Chloride rigid 0.1 0.6
SAN Styrene Acrylonitrile 0.3 0.7
SAN 20% GF Styrene Acrylonitrile 20% glass fiber 0.1 0.3

Injection processing:

Regarding control of the injection technology, the causes of sink marks include: insufficient pressure, excessively slow injection speed, small gate or long runner. Therefore, when using the injection molding machine, it is necessary to pay attention to the molding conditions and whether the holding pressure is enough to prevent the appearance of sink marks.

The sink marks on a hard-plastic product are usually caused when the molten plastic shrinks due to cooling, but at the same time sufficient melt is not provided through the gate to fill up the space created by concentrated shrinkage. Therefore, factors that are not conducive to shrinkage compensation will affect our solution for the sink mark issue.

Most people know that it is easy to cause sink marks when the mold temperature is too high. Therefore, they usually prefer to solve the problem by lowering the mold temperature. However, sometimes if the mold temperature is too low, it will not be helpful for solving the problem of sink marks.

When the mold temperature is too low, the melt is cooled very fast. For the thick part that is far away from the gate, sufficient shrinkage compensation will not be possible, since the passage in the middle section is blocked due too fast cooling, thus making it harder to solve the sink mark issue. Sink marks on larger and thicker molded products are particularly serious. Therefore, when dealing with tough sink mark issues, it is helpful to check the mold temperature. Each material has its proper mold temperature.

It is not conducive to solving the sink mark issue when the melt temperature is too low

Similarly, most of us know that a plastic injection molded product is prone to the sink mark issue when the melt temperature is too high. If the temperature can be properly lowered by 10 to 20°C, the sink mark issue will be improved.However, when the injection molded part has a sink mark in a relatively thick part, then setting the melt temperature to a too low level, e.g., close to the lower limit of the melt temperature, will not be helpful for solving the sink mark issue, or even make worse. The thicker the injection molded part, the more obvious it is. PC material is a raw material that solidifies quite quickly, so its sink mark issue can be said to be a big problem in plastic injection molding.Also, if the melt temperature is too low, it will not be conducive to increasing the overall shrinkage amount, resulting in an increase in concentrated shrinkage, thereby exacerbating the sink mark issue.

To solve the sink mark issue, the first thing that comes to mind is to raise the injection pressure and extend the injection time. However, if the injection speed is already very fast, it will not be conducive to solving the sink mark issue. Therefore, when it is difficult to eliminate the sink mark, it should be solved by lowering the injection speed. When the injection speed is lowered, a large temperature difference can be created between the melt front and the gate, which is helpful for melt solidification and shrinkage compensation from the far end to the near, while also allowing the sink mark far away from the gate to get a higher pressure for shrinkage compensation, thus helpful for the problem solving. Due to the lowering of the injection speed, the temperature of the melt front is relatively lower, while the speed has been slowed down, so it is not easy for the molded part to flash. The injection pressure and time can be further increased, to better solve the serious sink mark issues.

Mold & Product Design

The mold runner and cooling designs greatly influence the final product. Due to the low heat transfer capacity of the plastic material, it solidifies and cools slowly. There should be enough plastic to fill the cavities, so that the plastic does not flow back to cause pressure drop when the screw of the injection molding machine is performing injection or pressure holding.

On the other hand, the gate cannot solidify too fast, so that the semi-solid plastic will not block the runner and cause pressure drop, and subsequently sink marks on the product. Different mold flow processes lead to different shrinkage rates. The properly controlled barrel temperature is able to prevent the overheating of the plastic part; extending the cycle is able to allow sufficient time for the product to cool down.

How much does injection molding cost?

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The cost of injection molding is influenced by a multitude of factors, but is mainly comprised of the following:

  1. Raw material cost – This cost is quite easy to be calculated. Ask the raw plastic material supplier how much 1kg costs, multiply the product weight by 3% of loss rate, and then multiply the raw material price to get the cost of the raw material;
  2. Machine cost – Regarding this cost, ask a plastic injection molding factory what the hourly processing rates of different plastic injection molding machines are? Assume that the processing cost per hour for a 100-ton plastic injection molding machine is 60 RMB/hour, then the cost per minute is 1 RMB; at this point, it is necessary to calculate the injection molding cycle of the plastic part, as well as the number of cavities of the mold. Assume the injection cycle of the plastic part that you are evaluating is 30 seconds, then there are 60/30 = 2 shots in 1 minute, which means that two rounds of molding can be achieved in 1 minute. And, assume it is a two-cavity mold, then the machine cost of the plastic part is 1 yuan divided by the number of shots in 1 minute, and then divided by the number of cavities in the mold. So, the final machine cost is 1 RMB/ 2 shots / 2 cavities = 0.25 RMB / piece.
  3. The secondary processing cost includes painting/screen printing/electroplating, etc. You may ask their respective processing plants for the figures.
  4. Packaging costs – According to the size and volume of the plastic part, the cost of the carton/bag can be obtained;
  5. Transportation cost – According to the delivery location and the cost of the container truck, the transportation cost per piece can be obtained by dividing the total loading amount;
  6. Other expenses: Because the above costs do not include the costs of indirect personnel or other related personnel, it is necessary to add some fees according to the different conditions of each factory;

The profit equals the total sum of the six items mentioned above multiplied by the profit rate of 10-30%. Then you can get the final cost of a plastic part. The profit should be determined on the basis of the situations in each factory and the order amount.

injection molding cost in china

A Injection mold price calculation method!

Mold price calculation

  1. Empirical calculation of mold price = material fee + design fee + processing fee & profit + VAT + mold trial cost + packaging & transportation fee, of which the percentages are usually:

Material fee: materials and standard parts account for 15%-30% of the total mold price;

Processing fee & profit: 30%-50%;

Design fee: 10%-15% of the total mold price;

Mold trial: for large and medium-sized molds, the cost can be controlled within 3%, and for small-sized precision molds, within 5%;

Packaging & transportation fee: can be calculated in real terms or by 3%;

VAT: 17%

  1. Material coefficient method – The mold material fee can be calculated according to mold size and material price. Mold price = (6~10) * material fee

Plastic mold = 6 * material fee

Die-casting mold = 10 * material fee

Cost accounting for plastic injection molding

Cost of a molded part = material fee + processing fee + packaging fee + transportation fee

Description:

  1. Material fee = [(1 + material loss) * product weight * batch size + material loss during machine adjustment + normal scrap rate * product weight * batch size *] material price / batch size

The material loss is generally 3%-5%; the material loss during machine adjustment and the normal scrapped product usually weigh 5,000g-15,000g.

  1. Processing fee = (machine adjustment time / batch size + molding time / number of mold cavities) * processing cost of the injection molding machine

At present, processing cost of injection molding machine in Shenzhen is calculated by tonnage (domestic equipment)

Tonnage of Machines 80 120 160 200 250 300 400
Cost per hour(RMB) 35-45 65-85 80-110 95-140 150-200 180-220 250-300

Calculation of molded part price – Specifically, the quote for a plastic injection molded part is shown as follows:
Product unit price = material price + processing cost
Material cost = (actual weight + loss) * material unit price
Processing cost = molding cycle * unit price (seconds) ÷ number of cavities (that is, the price of each piece)
If packaging is specifically required, the cost of packaging needs also to be added.
Basically, these are the three major categories.
The material price is relatively simple: PP or ABS is directly calculated as the price * product weight, while that of a colored piece can be calculated on the basis of the raw material price. The price of a black part can be calculated according to the specific recycled materials or product requirements. The processing cost is correlated to the number of mold cavities, the molding cycle and the weight of the product; the machine cost can be detailed to price per second according to machine tonnage. Assume that the number of mold cavities is large, the weight is heavy and the molding cycle is short, the processing cost will be low, accordingly leading to a low unit price.

On assumption that a PP product weighs 50g, make calculations respectively using 1*1 / 1*2 / 1*4. The product is a colored piece made of the new material.cycle time is 60 second.the injection machine is 100 Ton,and cost 60RMB per hour.PP Raw material is 12 RMB per kg.

1*1(1 cavity mold):   

Material cost:0.05×12=0.6RMB ;  processing cost:60/60/1=1RMB; so injection molding price:0.6+1=1.6RMB

1*2(2 cavities mold): 

Material cost:0.05×12=0.6RMB ;  processing cost:60/60/2=0.5RMB; so injection molding price:0.6+0.5=1.1RMB

1*4(4 cavities mold):

Material cost:0.05×12=0.6RMB ; process costing:60/60/4=0.25RMB; so injection molding price:0.6+0.25=0.85RMB

Rapid prototyping play a very important role in China product development

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Study shows that 80% of the production cost is determined at the design stage. Therefore, the design stage is of great importance to product cost control. Rapid prototyping constitutes an important part in the industrial design process. From the fully manual prototyping (hand sampling) to the semi-mechanical prototyping, then to the modern 3D printing of prototypes, the progress epitomes the technological progress of the modern manufacturing industry. Among them, though Rapid prototyping is an advanced supportive design technique, it doesn’t receive enough attention.

rapid prototyping in china

It has been proved th Rapid prototyping not only plays a very important role in product design decision, but is also an effective tool for protecting product information and marketing.

Now, let’s talk about the importance of Rapid prototyping from different stages of the industrial design process

  1. Design Optimization

Mechanical parts that are more focused on geometric shapes can be designed directly with the application of computer graphics. For products with curvy surfaces, such as small-sized household appliances, on the one hand, the reverse engineering technology can be leveraged for 3D mapping, to obtain the 3D modeling data. And, after adjustment, the 3D data obtained can be directly copied with the help of the computer-aided rapid prototyping technology. The benefits of this approach are more evident when designing artworks that feature varied curvy designs. Firstly, the designer directly creates the shape with materials such as sludge, and then parameterizes the prototype through a 3D scanning device to obtain the computer data of the original prototype, which is then copied to a rapid prototype, to greatly improve the design efficiency

  1. Design Discussion

During the product design process, discussion plays a very important role. Visualization is an important part in the expression of product design, as well as the cornerstone for design discussion. Modeling products quickly and efficiently is able to ensure a higher design efficiency within the same period of time. During the design creative stage, what is used the most is often the 2D expression based on drawings. However, in the middle and late stages, the design expression will be more specific, so a more intuitive prototype should be adopted as the subject of discussion. Compared with the 2D expression, the hand sample enjoys an irreplaceable advantage, because it is able to make the details of the product clearer and the visual perception of the product more intuitive. Since everyone in the design team is able to see these designs, obvious advantages are demonstrated in the coordination of teamwork among all members.

  1. Functional Test

Rapid prototyping is able to help with certain functional tests and simulate the final form of the product, including functions and curves, etc. Prototyping allows the designer to obtain the most intuitive understanding of the dynamic simulation and internal structure of the prototype. When materials with a certain strength are used, a functional prototype containing an internal structure can be made to verify whether the product structure is reasonable, whether the wall thickness meets the requirements, and whether the moving parts are smooth enough, etc. A prototype can also be used for aerodynamic testing. For example, in the design of fast-moving objects, such as cars, high-speed trains and spacecrafts, a 1:1 prototype can be made and placed into a wind tunnel for intuitive aerodynamics research.

  1. Cost Cut

A design defect that is identified with a CNY 1,000 worth of prototype may cause a huge loss of up to CNY 10 million to produce and test, if the product is put into production and launched into the market. Through hand sampling, the final shape, size, structure and color of the product can be obtained, or product ergonomic testing can be performed at a lower cost. Also, important product information, such as product volume and quality, can be predicted, which can effectively help with the control of the packaging, transportation and material costs during production. Also based on this, the sales price and profit of the product can be estimated. If the cost exceeds the assumptions at the beginning of design, adjustments can be made in a timely manner until the specified target range of cost is reached. Therefore, Rapid prototyping is an effective means for an enterprise to control the cost.

  1. Market Research

In a trade fair, the 2D display board or the 3D animation you show to your potential customers will not be as attractive as the prototype. The prototype can most intuitively indicate the shape, color, size, structure and function of the product. You can also use the rapid hand sampling technology to reproduce the prototypes in small batches, and then send them to different regions for investigation, so as to obtain differentiated survey data. The hand sampling technology is able to help predict the actual consumer mindset and application effects of the product before mass production.

Generally speaking, with the advancement of modern processing technologies, the Rapid prototyping technology is continuously improved with a declined cost. On such a basis, more attention should be paid to the role the rapid prototyping plays in the whole process of industrial design, to make full use of its advantages, thus improving design efficiency and reducing R&D risks.

Benefits of the 3D Printed Prototype:

  • It takes only a few to tens of hours to finish the production of one or several prototypes, so the product development cycle can be reduced by more than 40%;
  • There is no need for mold machining, or mold development. You can print prototypes directly and quickly, to greatly reduce product development costs;
  • Dimensional accuracy is able to meet the requirements of industrial grade assembly. The dimensional accuracy of a plastic sample can reach up to ±0.1mm, while that of a metal sample can reach ±20μm;
  • The plastic sample is made of the high-quality engineering plastic material, the nylon 12, which boasts such excellent properties as high strength, high toughness, as well as high resistance to wear, corrosion and temperature.
  • Rapid prototypes are able to meet a wide range of demanding test requirements, such as wind tunnel testing (3,000rpm), water pressure and flow testing (10,000+ cycles);
  • A variety of complex curves and special structures are available at one stroke.

Different mold cooling channel design cause different cooling effect

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Many believes that the special-shaped cooling channel is not effective at all, but is a kind of deceptive technology! As a matter of fact, the point is not that the special-shaped cooling channel is not effective, but where you choose to place the cooling channel is still arguable. Let’s take a look at the example below:

Figure 1 shows the same part, coming with special-shaped cooling channels designed by different designers. Although all of them adopt the special-shaped design, they perform differently with regard to mold temperature improvement. See Figure 2, let’s verify this using the CAE software. We can find that some of the designs give a great performance as shown in Figure 4, but some others are not so satisfactory as shown in Figure 2. So, what is the problem?

The cooling channel shown in Figure 2 is too densely designed, so when the coolant enters the cavity, it will first take away some of the local heat, not to mention the problem lying in structural strength. At the same time, this amount of heat is kept circulating, which in fact cannot fulfill the function of cooling, but rather heat preservation. The design shown in Figure 4 is able to ensure that the coolant quickly flows to the areas that need to be cooled, while removing the heat from the mold in a fast manner, which is able to accelerate the cooling of the product. Therefore:

  1. The cooling channel needs to be smooth, without any branches, so as to ensure the optimal effect.
  2. It is not right to believe that the more cooling lines and the denser, the better – It is the most important to remove the heat from the mold ASAP.
  3. The shape of the cooling channel also affects the cooling effect.

mold cooling channel

heat emission of mold cooling channel

we have more cooling channel designs,please the below links for detail

Injection Mold Cooling Systems

Types of Food Grade Plastic Materials

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food grade plastic

PET

  1. PET

Usually, this plastic is used in the production of plastic bottles, beverage bottles and the like. The plastic water bottles and carbonated beverage bottles people often buy are packaging products made from PET, which is a food-grade safe plastic material.

  1. Potential Risks:

PET is only suitable for the packaging of room temperature or cold drinks, rather than overheated food. If the temperature is too high, the bottle will release toxic substances, which may cause cancer. If the PET bottle is in service for a long time, it will automatically release toxic substances, so the plastic beverage bottles should be disposed right away after use, and should not be used to contain other foods for a long time, so as not to affect health.

PP

The PP plastic is one of the most common plastics, and can be used to produce plastic food packaging, such as special plastic food bags, plastic food boxes, food grade straws, and food grade plastic parts, etc. It is safe, non-toxic and resistant to low and high temperatures. PP is the only plastic that can be placed in a microwave oven and boasts a strong folding endurance (50,000 times). When falling from a high altitude under -20°C temperature conditions, it will not break.

PP plastic bag: Polypropylene

Characteristics: Harder than OPP, stretchable (two-way stretch), able to be stretched into a triangle, bottom or side seals (envelope bag), and barrel. Its transparency is not as good as that of OPP.

HDPE

  1. HDPE

The HDPE plastic is commonly known as high-density polyethylene, which enjoys a high application temperature, hardness, mechanical strength and chemical resistance. It is a non-toxic and safe material that is often used to produce plastic containers for food.

High-density low-pressure polyethylene feels crispy, and is often used to produce plastic bags.

  1. Potential Risks:

Plastic containers made from HDPE are difficult to clean, so it is not recommended for recycled applications. It is better not to microwave it.

food grade plastics            food grade plastics

 LDPE

  1. LDPE

Low density polyethylene, commonly known as LDPE, is soft to touch.

The products made from LDPE are odorless, tasteless, non-toxic and matte. They are commonly used in food grade plastic parts, food grade composite packaging film, food wrap, medical and pharmaceutical plastic packaging.

  1. Potential Risks:

LDPE is not highly heat resistant, and usually melts when the temperature exceeds 110°C. For instance, don’t heat food wrapped with the household food wrap film, to prevent the oil contained in the food from dissolving the harmful substances in the wrap film.

 PS

  1. PS

It is often used to produce bowls of instant noodles, fast food boxes, disposable food packaging boxes, etc., and is very cold resistant.

  1. Potential Risks:

The PS box cannot be microwaved, so as to prevent the release of toxic substances caused by excessive temperature. It also features poor resistance to acid and alkali, so not suitable for containing acidic foods, to avoid release of carcinogens.

 PC

  1. PC plastic resin

This plastic material can be used to produce sports water bottles, etc., and is widely used in the production of plastic containers as a safe material.

  1. Potential Risks:

There is residual bisphenol A (hazardous substance) contained in PC.  The higher the temperature, the more and faster it releases. Therefore, do not use PC water bottles to contain hot water, so as not to increase the speed and density of bisphenol A (if any) release.

 PVC

  1. PVC：

Currently, PVC plastics is rarely used for food packaging, so it is better not to buy it.

  1. Potential Risks:

When this material is used under high temperature conditions, or even during the manufacturing process, it is easy to produce and release harmful substances. When toxic substances enter the human body along with food, it may cause such diseases as breast cancer and birth defects. At present, containers made from this material is seldom used for food packaging. If you are using it, don’t get it heated.

How to control the cost of plastic injection molding?

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The cost control of plastic injection molding also involves many factors. It must be controlled from the equipment, application process, raw material, as well as management and technology to achieve the optimal efficiency at the lowest cost.

Plastic injection molding company from China

Tools and Components Control:

Tools – All screws, nuts, nylon hoses and hose clamps, etc. in the packaging workshop must be controlled with a corresponding method, or great waste will be caused!

 

Mold Application Control:

Production Process:

  • Appropriate clamping pressure during the adjustment process – It is appropriate as long as the product meets the requirements, and the clamping force is able to ensure that the injection pressure does not force the core and the cavity open to cause flashing.
  • The ejection speed needs to be properly controlled. The ejection system itself is a system that should avoid as much friction as possible. If the speed is too fast, the system will inevitably be damaged.
  • Make full use of the low-pressure protection feature of the injection molding machine, so that there is chance for the mold to be damaged.
  • Too-high or uncontrolled injection pressure, speed, holding pressure and back pressure are also important factors that cause damage to the mold or affect its service life!
  • Mold temperature control is also very important. Excessive mold temperature will cause the individual parts inside the mold to swell and the compatible space to change, thus finally damaging the mold. The too-low mold temperature is not able to ensure the mold temperature to reach a relative balance after the mold absorbs the heat generated by the melting of the plastic, thus eventually causing rust and damage due to long-term moisture in local areas!
  • Human factors: Especially when such issues as mold adhesion or scratches and other common mold issues occur, a specialist is required to handle them. Do not arbitrarily authorize anyone to handle them casually.

Maintenance & Storage:

  • During the production process, the moving parts such as the lifter, the side pin, the slider, the guide pin and the ejector pin must be thoroughly lubricated at least once a day, or more than twice a day in special circumstances.
  • During hot-oil production, it is necessary to pay attention to the clamping of the mold and the partial swelling of the slider. During cold-water or icy-water production, the coolant must be cut off at least 15 minutes before shutting down the machine!
  • Pay special attention to the matte-surfaced mold and the polished mold – don’t damage or scratch them, or it will be quite troublesome to repair them!

 

Application of the Injection Molding Machine:

Plastic Injection Options:

  • Injection Volume:During the production process, the choice of injection molding machine is usually to ensure the molding quality. The weight of the product should be 25-75% of the total weight of the injected plastic, which is the recommended ratio. If the best product volume is required, the range should be lowered to 40- 60%.
  • Wear- / Corrosion-resistant Barrels and Screws:If the glassfiber-reinforced hard plastic is selected, it is better to choose wear- / corrosion-resistant alloy barrels and screws. Wear tends to occur when common nitrided screws are employed: choose corrosion-resistant alloy screws and barrels for acidic materials, such as PVC and POM.

Cost Control during injection molding Machine Adjustment:

  • Reduce wear and tear:If abnormal wear and tear is caused due to improper operations or other accidents during the adjustment process, the machine will not be able to operate properly for 12 years. Eventually, the daily wear and tear will increase greatly, and at the same time lead to incalculable and serious maintenance costs! To reduce abnormal wear and tear, it is necessary to strengthen the technical level of the technicians, as well as the knowledge of other workers.
  • The choice for the switch point between injection and pressure holding is able to reflect the actual operation level of a technician in an injection molding workshop. When realizing that the most fundamental purpose of pressure holding is to compensate for the shrinkage, the injection time and pressure can be minimized to reduce wear and tear, as well as power consumption, thus finally achieving the requirements for cost control!
  • The mold opening and closing process also reflects the actual operation level of a technician in a plastic injection molding workshop, because it fully reflects the connection between speed, time and energy consumption!

 

Material Cost Control:

The key to the cost control of a plastic injection molding workshop is the material control. If material control fails to reach the target, it will directly lead to a serious decline in profit. Any carelessness may lead to loss of profit.

Starting from the plastic materials release, control every detail to ensure zero material waste.

  • The machine cleansing process: Firstly, the machine scheduler must schedule the production from light to deep colors, so that it is possible to eliminate the discoloration that may occur by using a deep color to cover a light color. When cleansing the machine, first try to cleanse the machine with prepared sprues or recycle materials, and then adjust the machine using the sprues of the material to be used. When the product reaches the required quality, the production officially starts.
  • Machine adjustment process: Try to use the parameters and instructions provided by the flowchart, making the adjustment process a process of copying the book or inputting the parameters, thus simplifying the general adjustment process.

Surface finish of plastic injection molding product

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surface finish of VDI3400 texture
VDI 3400 texture

Different physical and chemical properties of the polymer blends, as well as the different parameters of the plastic injection molding process cause the surface finish on the plastic composites to vary greatly.

For a plastic injection molding service provider that offers custom-made products, the first goal is to work in collaboration with the client to determine the importance of surface finish for the exterior appearance, as well as the performance of the injection molded product, or to be specific, is the final product an eye-catching piece or simply a functional one? Your answer to this question determines the choice of material and the option of surface finish, based on which the plastic injection molding process is set, and the secondary finishing operations are accordingly required.

Available Surface Finish Types

Before making your final decision on the surface finish type for your plastic injection molded product, you should first have a clear idea in mind of what type of mold you need on the basis of your production volume, as well as the type of the material that your mold is going to be made of. Usually, a steel mold is of a higher hardness than an aluminum one, thus able to offer more surface finish options, because the steel material possesses the benefit of being able to be polished for a surface finish that is smoother than other materials, which is also helpful for such secondary finishing operations as painting aimed to enhance your final molded products.

Available surface finish types include:

  • Geometric shapes / patterns
  • Grains, e.g., the leather texture
  • Secondary finishes, e.g., paintings, print, etc.
  • Etching
  • Sand blast
  • Glossy, matte, or satin finishes
  • Mirror polishing or lens finishes

CATEGORIES of SURFACE FINISH

The Society of the Plastics Industry (SPI) has standardized the surface finishes for plastic injection molds. According to the finishing process selected, the following grades are determined:

Finish SPI* standard Finishing Method Typical surface roughness Ra (μm)
Super High Glossy finish A-1 Grade #3, 6000 Grit Diamond Buff 0.012 to 0.025
High Glossy finish A-2 Grade #6, 3000 Grit Diamond Buff 0.025 to 0.05
Normal Glossy finish A-3 Grade #15, 1200 Grit Diamond Buff 0.05 to 0.10
Fine Semi-glossy finish B-1 600 #Sand Paper 0.05 to 0.10
Medium Semi-glossy finish B-2 400# Sand Paper 0.10 to 0.15
Normal Semi-glossy finish B-3 320#Sand Paper 0.28 to 0.32
Fine Matte finish C-1 600 Grit Stone 0.35 to 0.40
Medium Matte finish C-2 400 Grit Stone 0.45 to 0.55
Normal Matte finish C-3 320 Grit Stone 0.63 to 0.70
Satin Textured finish D-1 Dry Blast Glass Bead #11 0.80 to 1.00
Dull Textured finish D-2 Dry Blast #240 Oxide 1.00 to 2.80
Rough Textured finish D-3 Dry Blast #24 Oxide 3.20 to 18.0
Machined Marks – – 3.20 (with visible machining marks)
surface finish SPI standard
SPI standard

AESTHETICS or FUNCTIONALITY

In surfacing finishing, a balance needs to be achieved between aesthetics and functionality, because the surface finish is able to affect not only the friction coefficient, but also the resistance to wear and tear; if these are considered to be important characteristics for the product performance, the design team is then required to choose the material and process that helps create a well matched finish effect. A skilled plastic injection mold maker is equipped with tremendous scientific data with regard to material chemistry, material behavior, and process conditions, so as to get the reference for accurate choice of surface finish process on the basis of specific parameters.

It is of critical importance to decide the surface finish type as early as the design stage, because it has a great influence on your selection of material and tooling, as well as your choice of the finishing process. The surface finish of a product is limited by the textures on the tool steel. From time to time, the imperfections, such as sink mark, on a surface can be covered by a rougher texture pattern. In addition, the draft required on a molded part can also be affected by the surface finish – if the draft is not appropriately designed, the surface finish could probably be destroyed during the ejection process.

SELECTION of PLASTIC MATERIALs

Your choice of the material, the additive, and the different plastic injection molding parameters, such as the fill rate, as well as the injection pressure and temperature affects the 2 key surface characteristics of glossiness and roughness. What is of special importance is the type of the material, e.g., the higher the melt temperature of the products made from reinforced crystalline resins, the more glossy and less rough the surface is, thus creating a smoother effect. However, when being plastic injection molded, a higher mold temperature is able to improve the glossiness and reduce the roughness of the reinforced amorphous resins.

Also, with regard to surface finish, another critical consideration is the additive that is applied to the resin material. At this point, the knowledge of material science is truly brought into play, e.g., the addition of contents containing fiberglass will lead to a lower glossiness. On the other hand, such additives as the carbon black and mica are able to reduce surface roughness, meaning if you have to maintain a certain degree of surface roughness out of considerations for product performance or appearance, you need to avoid or at least find substitutes for these additives. Also, if you add particulate fillers, the surface roughness might be increased. To produce a specific surface finish, a qualified engineer should be able to mix and match the proper combination of resins with additives.

China mold manufacturing business status compare to other countries

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Over the past decade or so, China mold manufacturing technology has made a qualitative leap, and the mold manufacturing industry has grown rapidly from small to large, making China one of the biggest mold manufacturing countries in the world. Along with the development of China’s automobile industry, the rise of domestic auto brands to the middle and high-end market segments, and the emergence of new energy vehicles, the market has put forward new demands for us, which requires us to move from low-end molds to high-end molds, and from a large mold manufacturing country to a mold powerhouse.

injection mold manufacturer in China

At present, the mold production value of the six mold manufacturing countries, i.e., China, the US, Japan, Germany, South Korea and Italy, occupies an absolute position in the world, among which the mold production value in China is the highest of all.

  1. The US

At present, there are about 7,000 mold manufacturers in the US, most of which produce automotive molds. Factories with less than 15 workers account for about 60% of the total, those with 15-50 employees account for 30% of the total, and the rest account for 10%. In spite of the small number of workers, thanks to its advanced automation and process technologies, it is now already one of the leaders in the world. According to authoritative statistics in 2014, the output value per capita of the US mold industry is around CNY 1.27 million.

  1. Japan

At present, there are about 10,000 mold enterprises in Japan, most of which produce automotive molds. Among them, individual companies with less than 20 workers account for 91% of the total. This is quite a shocking number, from which it is not difficult to see that the Japanese mold factories are usually small in size, and they mainly develop towards modularization. For example, a car needs 8,000 stamped parts, and each factory produces several fixed parts, which are then assembled, so as to lower the cost and improve efficiency.

  1. Germany

Germany is a country with very developed machinery and one of the first countries in Europe and America to start making molds. Its mechanics is almost invincible in the world, and the same is naturally true with mold making. Most of the factories produce automotive molds. There is a jargon in Germany: coordination, teamwork, technological innovation, learning from each other’s strengths, making progress together, giving full play to the overall advantages and jointly becoming the industry leader. You know, many countries may probably stand in awe before this sentence of courage and insight.

  1. China

Throughout the past decade, it can be said that the China’s mold manufacturing industry has undergone earthshaking changes. China boasts the highest number of mold factories, about 30,000 in total, among which state owned companies account for 5%, JVs account 10%, while the rest are privately owned. At present, there are about 3 million people involved in the mold industry.

Although the Chinese data seems amazing, with regard to production capacity per capita, we can see that the annual production capacity per capita in Germany is 2 CNY million, that in the US and Japan are respectively CNY 1.27 million and CNY 1.2 million, but that in China is only CNY 335,000. The comparison result is really shocking. The annual output value per capita of the mold industry in the US and Japan is 3-5 times that of China, and the annual output value per capita in Germany is 5-9 times that of China.

In recent years, with the continuous upgrading of household consumption, the development of China’s automotive industry has been accelerated. The development of automobiles has driven the rapid development of the automotive mold industry, and many enterprises have transformed towards the automobile industry. So, the China’s automotive mold industry is booming, with great prospects.

Moldflow Analysis Report for plastic injection molding

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Moldflow analysis is the plastic injection molding simulation software that obtains data and results  through the computer-aided simulation to simulate the plastic injection molding process, based on which, the feasibility of the mold solution is to be evaluated, in a bid to improve mold and product designs.

plastic product for mold flow

Product description

Wall thickness and mesh statistics in moldflow analysis

mesh thickness diagnostic moldflow

Thickness are uniformed

Plastic material information

Plastic material information for moldflow

injection molding process analysis for moldflow

Initial Nozzle/Gate Locations and Circuit

Gate location for moldflow analysis

Filling

filling moldflow analysis

The filling process is balance

Distortion, all effects at Z Component

In this plot a scale factor of  2X was added to overstate the magnitude of the warpage to make the trends easier to understand。

1) 4 gates injection

4 gates Distortion analysis

Deflection of Z direction is large  NG

2)2 gates injection

distortion analysis

Deflection of Z direction is large  NG

3)One gate hot runner injection

distortion moldflow analysis

Deflection of Z direction is large  NG

4)Change material to ABS Chimei PA757,4 gates

deflection analysis

Deflection of Z direction is small  OK

Conclusion:

As can be seen from the above results of moldflow analysis, four-point glue injection is smaller than two-point glue injection, but the deformation is not significantly improved. After replacing PP with ABS, the deformation is significantly reduced. It is suggested to use ABS material forming to reduce product deformation.