Jackie, Author at Ecomolding.com

The runner design

March 10, 2020August 27, 2018 by Jackie

The Runner Design Concept

The runner refers to the melt flow passageway between the end of the main runner and the gate, which is used to change melt flow direction and allocate it to each cavity in a stable and balanced way.
The basic design principle of the branch runner is little pressure/heat loss, with the minimum quantity of plastic retained in the runner.
Sectional Shapes of the Branch Runner:

–Circular, with the minimum specific surface area (runner surface area/runner volume), but during production, both sides of the mold plate need to be aligned.

–The commonly applied forms, trapezoid and U-shape are easy to process.

–Semicircle.

–Rectangle, larger specific surface area and high resistance to flow, thus seldom applied.

The Principle of the Runner Design

The runner is usually designed on either half of the plastic injection mold.
When considering the layout of the cavity and the branch runner, it is better to ensure that when projected on the parting surface, the geometric center of the total projection area of the cavity and the runner overlap with the center of the clamping force.
The internal surface roughness of the branch runner is 1.6. In this case, the outer layer melt flows faster than the inner layer melt inside the branch runner, which tends to cool down and thus form a heat insulation layer.
The sectional size of the branch runner is dependent on the plastic part size/type, injection speed, as well as the length of the branch runner.
Generally, when the diameter of a branch runner is smaller than 5 – 6mm, runner size will have a greater influence on fluidity; when the diameter is greater than 8mm, there will be little influence on fluidity.
If the branch runner is very long, it might be better to further extend the branch runner along the flow direction to form a cold slug well, so that the cold materials will not enter the cavity.
The branch runner cannot be too thin, or temperature/pressure loss will increase, which makes it hard to fill up the cavities far from the main runner.

The Runner Design Layout

In a multi-cavity layout, it needs to be guaranteed that the molten plastic can concurrently fill up each cavity in a uniform way. There are 2 layouts, i.e. balanced and unbalanced:

Balanced: uniform filling, with each cavity concurrently filled.

Unbalanced: The runner is designed to be short to save raw materials.

Injection mold sprue bush (Main Runner) design

October 6, 2019August 26, 2018 by Jackie

Mold sprue bush,AKA.The main runner refers to the melt flow passageway from the joint between the injection molding machine nozzle and the mold sprue bushing to the starting point of the branch runner.

–The design has to minimize melt temperature drop/pressure loss.

–Adopt the cone shape design, to facilitate removal of the condensed material

Forms of The Mold Sprue Bush

Fixing Methods of the Mold Sprue Bushing

The main runner is usually located along the center line of the plastic injection mold, overlapping with the axle of the injection molding machine nozzle.
In horizontal and vertical injection molding machines, the runner axle should be perpendicular to the parting surface.
To facilitate removal of condensed materials from the main runner, the main runner should be designed into the cone shape, with a cone angle of 2 – 6º; the diameter of the smaller end D ＞ d + (0.5~1mm), d refers to the diameter of the injection molding machine nozzle.
The internal surface roughness of the main runner Ra ＜ 0.4; and the length of the main runner usually ＜ 60mm.
The transition between the bigger end of the main runner and the branch runner should adopt an arc-shaped design, of which the corner radius is 1 – 3mm.
Since the main runner is the first contact point of the high temperature molten plastic, which also frequently make contact with the injection molding machine nozzle, damages by collision tend to occur. Generally speaking, the sprue bushing needs to be fixed to the fixed clamp plate. See the following figure for the structure of the sprue bush.
The hardness of the mold sprue bush should be lower than that of the injection molding machine nozzle.

O-ring

October 7, 2019August 24, 2018 by Jackie

What is the O-ring used for?

In a mold structure, the cooling channel tends to leak at the joints between mold plates as well as those between the mold plate and the core insert due to the existence of joint gaps. To prevent this from happening, O-rings are often applied to seal the joints.

Mold structure design should take the following principle into consideration in case O-rings are applied:

Ensure sufficient positive pressure between the mold plate and the core/Cav insert.

Please click below for O-ring detail

HASCO O-Ring size and spec.

Injection mold sliders designing

December 16, 2019August 22, 2018 by Jackie

1. When designing the injection mold sliders, the biggest clearance between the slider and the product should be at least 2 – 3mm.

The inclination of sliders should be kept between 15 and 25 degrees, and the inclination of the guide pin should be 2 degrees smaller that of the wedge. The available diameters of the guide pin are 6mm, 8mm, 10mm and 12mm, with the min and max values being 6mm and 12mm respectively. If a slider width is larger than 60 mm, deployment of 2 angle pins needs to be considered; if the width exceeds 80mm, a guide bar needs to be placed under the slider in middle.
If the injection mold sliders is too high, the starting point of the angle pin hole needs to be lowered, so as to ensure smooth travel of the slider. If slider open/close time needs to be delayed, the diameter of the guide pin hole will need to be enlarged.

When the injection mold sliders are deeper in the cavity than its own length, a wedge will not be necessary. The inclination can be designed on plate A directly. A R3 is required at the bottom. Besides, the slider doesn’t need a wear block.
When depth of the slider is mainly in the core, a wedge will be needed; if the part profile surface contacting the slider is large, or there’s kiss off or shut off on the slider, a reversed wedge should be applied and the inclination should be 10 degrees or above;
If the part profile surface contacting the slider is small, the slider can be designed as shown in Fig. 3.1.6, and the height of the wedge surface should be higher than 2/3 of the slider height.

The wear plate of the mold slider employs the 2510 steel, of which the hardness reaches up to HRC50°-52°. For all sliders with a thickness of over 50.0mm, wear blocks should be placed on the base and the back. These wear plates measure 5mm in thickness, and are 0.50mm higher than the mold base. And for all the sliders, a clearance is not needed along the travel direction of the slider (as shown in the following Fig.)

The width and height of the slider clamp – made from the 2510 steel with a hardness of up to HRC50-52 – are 20mm and 20mm respectively, while the length is dependent on slider.

Mold Slider Return and Fastening Method

For upward (including inclined ones) sliders, there are raised fine inserts and pins. When there’s an ejector pin under the slider, a spring can be applied to facilitate return.

Requirements for Spring Location Design

Spring is built in the mold core and the slider (see 3.4.1A, 3.4.1B and 3.4.1C)
If the travel distance of the slider is long with an installation length of over 50mm, the spring may be mounted outside.

Air/Hydraulic Cylinder driving

If the height of the guide pin is larger than 100mm (see Fig. 3.7.1A) and the cavity slider needs to be lifted before A and B plates separate from each other, a Air/Hydraulic cylinder may be applied to drive it (see Fig. 3.7.2B).

Design Standard of Slider Inserts (Pins)

Design Standard of Slider Stops

For the undercut of a circular product with sliders on 4 sides, a stop needs to be mounted to the slider insert. It is better to design a separate stop for each individual product if there are multiple products in a single mold.

Guide Pins of plastic injection mold

March 10, 2020August 20, 2018 by Jackie

There are many types of guide pin structures in plastic injection mold application, among which the standard structural design is shown in the figure below. A guide pin has to serve as the cylindrical surface of concentric circles of different diameters. Based on structural dimensions and material requirements, a round steel bar with an appropriate size can be directly selected as the material. In addition, the technical requirements of guide pins need to be satisfied during the machining process.

Fig. 8-2 Structural Shape of a Guide Pin

Technical Requirements of Guide Pins

(1) At the joint between the guide pin and the fixed mold plate, the diameter concentricity tolerance should not exceed 1/2 of the diameter tolerance in the working portion.

(2) The cylindricity tolerance of the guide pin in the working portion should be kept within requirements.

(3) After being machined, the precision, surface quality and thermal treatment of each part of the guide pin should meet the requirements specified in the drawing. When applicable, the carburized layer on the working surface is required to be uniform usually with a thickness of 0.8 – 1.2mm.

Machining Process of Guide Pins

(1) Material Preparation & Cutting. The commonly used material of the guide pin is the 20 steel (or select materials as per the drawing). After cutting, an allowance of 3 – 5mm should be retained for facing; and an allowance of 3 – 4mm for cylindrical turning.

(2) Facing & Centering. Turn one end, retain a turning allowance of 1.5 – 2.5 mm, and drill the centered hole; turn the other end to specific dimensional requirements and drill the centered hole.

(3) Cylindrical Turning. Roughly turn the cylinder, and retain an allowance of 0.5mm on each side for grinding. When applicable, groove the guide pin to specification.

(4) Inspection. Inspect the finish sizes of the previous steps.

(5) Thermal Treatment. Follow the process, and ensure a carburization thickness of 0.8 – 1.2mm. After carburization, the quenching hardness is 58 – 62HRC.

(6) Lapping. Lap the centered hole on one end, and then lap the one on the other end.

(7) Grinding. Apply cylindrical grinder and centerless grinder to grind the cylinder. After grinding, an allowance of 0.01 – 0.05mm should be retained for lapping.

(8) Lapping. After machining, the surface of the cylinder needs to be lapped to reduce surface roughness, thus meeting the surface finish requirements.

(9) Inspection. Inspect the finish size of each step.

Mold texture

March 10, 2020August 14, 2018 by Jackie

Mod texture Definition

Texturing refers to the process that produces various patterns on the surface of a metal product through chemiosmosis, such as stripes, images, wood grain, leather pattern and stain, etc., while also including sandblasting, which means spraying glass sands directly onto the surface of a metal product.

The Purpose of Mold Texture

Improve product appearance. The texturing process is able to camouflage part of the shrinkage, welding line, parting line and steps of slider, etc.
Product surface strength can be improved via texturing and sandblasting.

Varieties of Mold Texture

Sand Pattern

Characteristics: Fast process, low cost and able to produce fine and 2D patterns.

Satin Pattern

Characteristics: Fast process and able to be applied to a plane surface. Twice as durable as the sandblasting process, and able to cover the weld lines and sagging marks on a rough surface.

Leather pattern and others

Characteristics: Durable. Product surface is abrasion resistant though cannot be fixed completely. Able to remove burnt and rust marks caused by chemical gases through surface treatment.

Other textures include stone/geometric patterns, HNDS and HN3D which are not commonly used. This time, we are going to do the satin pattern.

Procedure of Mold Texturing

Cleansing

Clean the mold cavity surface, to remove surface oil/grease.

Sealing

Apply adhesive paper or corrosion resistant coating to the cavity surface that does not need to be textured, so as to prevent corrosion. This is the most time consuming step, during which the 3 commonly used sealing materials include: Thick adhesive paper, to cover the majority part of the cavity surface; thin adhesive paper, to seal the details; and corrosion resistant coating, to cover the area that adhesive paper fails to cover, e.g. complicated curvy surfaces.

Drying

Dry the anti-corrosion coating.

Surface treatment

Carefully wipe the cavity surface to be textured using absorbent cotton, to make it free from any dirt, thus ensuring the texturing effect

Texturing

Apply a coating to the cavity surface to be textured and then soak it in the corrosive fluid. During this process, attention should be paid to the texturing status. Repeated soaking is required to get the desired textures.

Sandblasting

Sandblasting serves 2 purposes: A). To remove the residue liquid on the cavity surface after cleansing, with ammonia and pressure washer; B). To tune the gloss of the texture; different levels of gloss can be achieved by using different sands and different pressure levels.

Post treatment

Cleanse the cavity surface and apply rust protection agent before delivering the mold parts back to the mold manufacturer.

Common Post-texturing Problems

Due to the fact that the mold cavity surface is roughened after texturing, the most common problems like scratches and stickiness to the cavity may arise. In some areas, the originally small draft angle will be made smaller after texturing, or even resulting in a negative draft angle sometimes, so scratches are often caused. During the ejection process, ejector marks tend to appear due to unfavorable mold release, thus greatly affecting the part appearance.

To resolve the problem of scratches and ensure smooth mold release, the textured surface usually needs to be sandblasted to reduce the texture depth and at the same time eliminate the acute angles caused by texturing. In the practical production scenario, it is very difficult to resolve the mold release problem by adjusting injection parameters, so release agent is usually applied to the textured surface to facilitate production. From the perspective of mold, the situation may be improved by increasing the draft angle in the scratched surface area/increasing the number of ejector pins.

A Brief Introduction to Ejector Pins Design

March 9, 2020August 6, 2018 by Jackie

The Purpose of Ejector pins:

Eject the molded part from the injection mold.

Considerations for the ejection system:

1. Ejector pin holes should be at least 3/32” away from other holes;

2. At least a clearance of 1/32” for pin holes on the ejector plate;

3. At least a clearance of 1/64” for pin holes on the mold plate;

4. All ejector pins should adopt the standard dimensions; the ejector base cannot be ground lower;

5. During the injection molding process of nylon, LDPE or PP, the diamter of each ejector pin must be measured, because flash might occur when the clearanc between the pin and the hole is greater than 0.02mm

6. All ejector pin holes must be vertical and glossy (Ra ~ 0.25μm);

7. For plastic materials like PP, PE and Nylon, hole diameter = pin diameter + 0.01mm; for plastic materials like HIPS, PC and ABS, hole diameter = pin diameter + 0.02mm;

8. Ejector pin should pass through the base plate, ejector plate and mold components in a straight downward way;

9. After all ejector pins are installed, the ejector plate should be able to slide downwards freely;

10. Labels in the same direction should be provided near the location of all ejector pins and screw heads, so as to prevent wrong installation;

11. All pins need to come with dowels, to prevent wrong installation (the application of square-shaped pinhead should be avoided, unless the distance between ejector pins are very small; it cannot adopt the symmetric layout, but only the one-sided way. Usually, the 1^st one should be applied; apply the 3^rd when there is not sufficient space);

12. Upon installation of ejector pins, everything needs to be checked before covering the back panel;

13. After installation of the supporter, use a flashlight to examine each rib and hole from the direction of the mold core, to see if there is any problem with pins or sleeve ejectors. Cover the back panel when everything’s OK;

14. When designing the location of ejector pins, in addition to guaranteeing sufficient ejection force, it has to be ensured that the product can be ejected in a straightforward way;

15. There are two types of ejector pins, i.e. though-hardened and nitrided;

15.1 Though-hardened – surface hardness is 65 – 74HRC, and steel core hardness is 50 – 55HRC;

15.2 Nitrided – the nitrided surface hardness is 65 – 74HRC.

Design of Runner Ejector Pins

Purpose:

Eject the gate/runner from cavity.

Forms of Pins

2.1 Option 1 (for general purpose)

2.2 Option 2 (for general purpose)

2.3 Applied to transparent materials like PMMA

Design of Ejector Pin Location

Pin Locations

1.1 The ejector pin should be 0.040″ – 0.100″ away from the top edge of the upper mold;

1.2 Try to place the ejector pin at the bottom of the product, such as the Pin A shown below. Try to keep a distance of at least 0.010” from mold core. Don’t place on the top (Pin B)

1.3 If an ejector pin has to be placed on a slope, Location “A” is the first option,followed by “B” and “C”, because a product tends to dislocate on a slope, and the ejector force may decline due to the existenc of the slope. If “C” is the only choice, small blocks should be added to increase ejection force.

1.4 To avoid the upper mold from being damaged by the ejector pin, the ejector pin has to be placed in location “A”.

1.4.1 The pin has to be ground lower for 0.0005”, for venting purposes;

1.4.2 A spring is needed under the return pin.

1.5 When product is too high or draft angle is too large, draw the ejection path on a layout plan, to help avoid mistake when placing the ejector pin. When the product has a large R, draw the tangent of the R on a layout plan, as a boundary for ejector pin placement.

1.6 Place ejector pins under ribs

Among the above-mentioned 5 methods, 1 is the best, and 5 is the worst.

Ejector pin location design

Commonly Seen Mainstream Injection Molding Machines Brands

March 10, 2020July 30, 2018 by Jackie

The injection molding machine industry has experienced rapid development across the whole globe. Especially, in the era when Chinese manufacturing industry develops at a very fast pace, many Chinese and foreign injection machine brands are widely used in enterprises which produce plastic products. Among them, the more famous ones include Chen Hsong from Hong Kong, Victor Taichung from Taiwan, Haitian/Haitai/Bochuang from mainland China, Mitsubishi/Toshiba/Sumitomo from Japan, and Demag/KRAUSS MAFFEI from Germany. Comparatively speaking, Japanese injection molding machines enjoy the longest service life while German ones follow the highest safety standards.

(1) German Demag Injection Molding Machine
Demag is a world famous injection molding machine brand of the German Demag Ergotech. Its main characteristics include: the hydraulic mold clamping structure and the computer-aided optimized location control of the injection machine match quite well with preset acceleration curves, to ensure the fast and balanced mold clamping action, thus keeping mold intactness and shortening cycle time. Its hydraulic ejection mechanism is very easy to assemble and disassemble, since there is no abrupt hose while the clearance between tie bars is big enough to accommodate large sized molds. The injection molding machine employs DFE, which has achieved a closed-loop oil pressure control, thus able to meet the requirements for any high precision and high response; at the same time, it is able to minimize energy consumption, thus meeting energy-saving requirements (saves up to 30% energy when compared with conventional injection molding machines); adopts the Ergotech Control unit, which allows to switch over from injection to holding based on the required time, pressure and flow; the value can be set as per percentage or input physical values; NC4 can be used to control exterior devices, with a special page provided to set various process parameters for quality control. All process control is completed automatically by the NC4 control system.

(2) German KRAUSS MAFFEI Injection Molding Machine

KRAUSS MAFFEI is a main high-precision injection machine brand of Germany. EX, the all-electric injection molding machine KRAUSS MAFFEI has launched possesses the characteristics of fast speed, high precision, cleanness, as well as energy saving. Though designed with a very short drying cycle time, it features very high precision, thus able to guarantee the quality of molded products.

(3) Japanese Sumitomo Injection Molding Machine

Sumitomo is the no. 1 injection molding machine brand of Japan, as well as the no. 1 all-electric injection molding machine brand of the whole world. The all-electric injection molding machines of Sumitomo rank top in the world for five years in a row when market share is concerned. Sumitomo has been engaged in injection molding machine R&D and manufacturing for more than 40 years and is always well-known to the world for its high speed and high pressure. After the all-electric injection molding machines have gained widespread application, Sumitomo has become the leader of the injection molding machine industry by virtue of its strong R&D and innovative capabilities. Currently, Sumitomo has developed countless propriety technologies, such as Direct Drive, Double Center Press Platens and DST-Press etc., which enable the company to give an outstanding performance in the industry. In recent years, Sumitomo produces approx. 5,000 all-electric injection molding machines per year, ranking no. 1 among the leading Japanese all-electric injection molding machine brands for 5 consecutive years.

(4)Hong Kong Chen Hsong Injection Molding Machine
Hong Kong Chen Hsong is one of the top-selling injection molding machine manufacturers in the world, with one unit sold in every 10min on average. The company boasts an annual production capacity of nearly 15,000 units, and the whole product lineup covers the clamping force ranging from 5 to 6,500t and injection volume ranging from 1 to 100,000g. With technological innovation as the core purpose, in the early days of its foundation, Chen Hsong independently developed the first two-color blow molding machine of Hong Kong, which attracted the attention of the players in the industry. In 1960s, Chen Hsong became the first one to invent the screw injection molding machine, laying a solid foundation for the company to become the leader of the injection molding industry. Coming to the 21^st century, the manufacturing technologies of Chen Hsong injection molding machines have reached the world top level. In recent years, Chen Hsong keeps launching new products and new technologies. In 2000, it launched Asia’s first PET preform injection molding system which included mold, injection machine and manipulator. In 2001, it launched the all-electric injection molding machine, and in Sept. of the same year, it launched the high-precision ultra-high speed injection molding machine.

(5)Victor Taichung Injection Molding Machine
Victor Taichung is a company in Taiwan China which has successfully developed the all-electric injection machine and realized SOP. Based on its more-than-50-year mature technologies for injection molding machine manufacturing, Victor Taichung has so far developed a complete set of injection molding machines that include five variants of 50t, 80t, 100t, 150t and 200t, as well as 11 modular combinations, which are being sold to the US, the UK, South Africa, Japan, Philippines and Malaysia, etc. In the future, it plans to launch medium-/large-size electric injection molding machines, including 250t, 300t and 350t, while extending the range of electric injection molding machines, so as to satisfy customer’s increasing demand.

(6)Ningbo Haitian Injection Molding Machine
Chinese injection molding machine manufacturers are mainly located in the southeast coast and the Pearl River Delta, among which the Ningbo region has been enjoying the strongest momentum of rapid development, so it is now the largest manufacturing base of injection molding machines in China, with an annual production capacity accounting for 1/2 of the total annual production in China and 1/3 of that across the globe. The Haitian injection molding machine series is one of the representatives. Founded more than four decades ago, Haitian Group has now become the largest production base of injection molding machines. As a high tech enterprise that’s specialized in the production of injection molding machines, Haitian is famous in the domestic injection machine industry for its high quality, high efficiency, high grade and economic returns. Its products include the plastic injection molding machines of nearly 100 types, of which the clamping force mainly ranges from 58 to 3,600t (injection volume ranging from 50 to 54,000g), boasting an annual capacity of nearly 10,000t, with both production and sales ranking no. 1 in the China market. The company has comprehensively introduced the world-class fully computer-aided and fully automatic processing centers from Japan, Germany, the US and the UK, so as to turn out the Haitian injection molding machine series with high precision and high quality, including five series of HTB, HTF, HTW, HTK and DH, and boasting more than 100 machine types, so as to meet the different needs of different customers.

Lifters or Sliders for Undercuts on Four Sides?

October 7, 2019April 13, 2018 by Jackie

As mold designers, we are all aware that, in normal circumstances, lifters are created for inner undercuts and sliders are created for outer undercuts. However, when we have undercuts on all 4 sides of a product, which makes it impossible to release the product by force, how should the mold be designed? See the following figure for the product. Shall we create lifters or sliders? Now, let me explain the mold design solutions for such products to all of you.

Design analysis

When coming across such products, we will firstly consider whether it is possible to create lifters. However, analysis shows that the undercuts in the 4 corners will not be able to be released with the help of lifters (lifters in the arrow direction).

Solution

Since lifters are not able to ensure complete release of the undercuts, we have to think about the design scheme that combines lifters and inner sliders. As shown in the figure below, green parts are inner sliders, and pink parts are lifters.

How it works

Mold core and cavity open a bit, then the slope of the wedge drives the sliders to move towards the center, so as to release the undercuts from the 4 corners of the product. At the same time, the lifters eject the product out while the undercuts are released completely. Finally, you can take the product out and close the mold for the next production run.

Injection pressure,holding pressure and back pressure

March 10, 2020April 11, 2018 by Jackie

1．Injection Pressure

Injection pressure is exerted by the hydraulic mechanism of the plastic injection molding system. This pressure is transferred from the hydraulic cylinder to the molten plastic through the molding screw, under which the molten plastic will be pushed to flow into the mold sprue (also known as the primary runner of some molds), the primary runner and the sub-runner via the nozzle of the plastic injection molding machine, and then finally get into the mold cavity through the gate. This process is referred to as the injection molding process or the filling process. The purpose of the pressure is to overcome the resistance occurring when the molten plastic is flowing; or to put it another way, the resistance occurring in the flowing process needs to offset by the pressure exerted by the injection molding machine, so as to facilitate smooth filling.

During the injection molding process, the injection nozzle features the highest pressure in a bid to overcome the resistance to flow throughout the whole process. After that, the pressure shows a trend of gradual decrease from the nozzle to the melt front as the molten plastic flows further. If the mold cavity vents well, the final pressure on the melt front will be equivalent to atmospheric pressure.

The injection pressure on molten plastic is influenced by a diversity of factors. To sum up, there are 3 categories: (1). Material factors, such a material type, viscosity, etc.; (2). Structural factors, such as type, quantity and location of the runner system, shapes of mold cavity and product thickness, etc.; (3). Molding process factors.

2．Value & Time of Holding Pressure

When the plastic injection molding process is drawing to an end, the screw will stop rotating but only keep moving forward. At this point, the injection molding process enters the pressure holding phase, during which period of time the injection nozzle continuously feed materials into the cavity, to fill up the empty space caused by product shrinkage. If the pressure is not held after the cavity is filled up, the product will shrink for about 25%. In particular, shrink marks will be left near the ribs due to enormous shrinkage. Usually, the value of the holding pressure is about 85% of the top injection pressure, which, of course, is subject to actualities.

3．Back pressure

Back pressure refers to the pressure that the screw has to overcome during its return action after injecting material. The application of a high backpressure helps distribute the pigments and melt the plastic, but at the same time, it also extends the screw’s return time, decreases the length of plastic fibers and raises pressure in the injection machine. As a result, the backpressure should be kept lower, usually not exceeding 20% of the injection pressure. Some injection machines allow backpressure programming to compensate for screw travel decrease, which will reduce heat input, causing the temperature to drop. However, since it is not easy to predict the changeable result, corresponding machine adjustment will a troublesome task.