Germany is one of the first countries in Europe to produce molds. Its mould manufacturing technology and quality have been recognized by users all over the world. It is well-known in the world and is one of the most important high-end mould suppliers in the world.
After years of practice and exploration, German mould manufacturing companies have formed a consensus: whole industry must be coordinated, teamwork, technological innovation, learn from each other's strengths, make progress together, and play a good overall advantage to achieve industry success.
In addition, in order to meet needs of rapid development of new products today, not only large companies have established new development centers in Germany, but also many small and medium-sized mould manufacturing companies have done so, actively carry out research and development work for customers. Germany has always been very active in research and has become an important foundation for its unbeaten success in international market.
In fierce competition, German mold industry has maintained a strong position in international market for many years, and export rate has been stable at around 33%. According to Verband Deutscher Maschinen- und Anlagenbau (VDMA), number of mould manufacturing companies is about 5,000, but country's mold industry structure is still dominated by small and medium-sized mould suppliers: 80% for 20 people or less, 19% for 20-100 people, and 1% for 100 or more. According to statistics, per capita output value of German molds in 2014 was about 2 million yuan.

 

Let's get to the point and start learning about design techniques.

Before formal mold design, following drawings or documents usually have:
1. Parts drawing;
2. Sample book of injection mold design and production;
3. Contract of design and manufacture;
4. Other
And to fully understand above information, unclear must be confirmed by customer.

Part drawing determines ultimate purpose of injection mold design and must be thoroughly understood. It usually consists of following parts:
Front view, plan view, side view, sectional view, detailed view, reference drawing, annotation, tolerance list, list of official marks, title bar, and other aspects in view process should pay attention to following aspects:
1. Tolerance requirements are strict;
2. Part that has an influence on mold structure;
3. Part of existing drawing that cannot be understood;
4. Matters highlighted in notes;
5. Special materials and heat treatment requirements;
6. Part of wall thickness is thin (t <0.6mm)
7. Wall thickness of parts is thick;
8. There is no special official requirements on appearance;
9. Three-dimensional surface part;
10. Designer, date, deadline, price, etc.

Part drawing is drawn in two dimensions, and it is converted into a three-dimensional shape in designer's mind through view, and hand-drawn stereo drawing is very helpful.
Prepare paper and pencil.
First, draw outline of product, and then draw a cross-sectional view of each part according to your own understanding of parts.
These are very important for determination of future parting surface and division of input. If conditions permit, it is better to use aids such as clay to help understand.

Title bar of parts drawing generally indicates tolerances in drawing, materials of parts, etc., and must be carefully studied.
1. Part name;
2. Name of drawing;
3. Figure;
4. Material (including shrinkage);
5. Sample, refers to detailed specification of material, such as manufacturer, trade name, resin code;
6. Scale;
7. Designer;
8. Change column;

(1), gate type, location, quantity
If there is no special requirement, plastic injection mold designer needs to obtain customer's consent after making decision.
(2), requirements for entering sub-line
Since entering sub-line will form a seam on the surface of product, affecting appearance, especially for folded part, plastic injection mold designer should follow specifications of part.
(3), provisions for defects such as scratches on the surface of molded products
Plastic injection mold designer should avoid mold structure design that may cause above defects.
(4), no tolerance requirements.
(5), change in shape and size of molded product requires consent of customer. As a plastic injection mold designer, it is not a discretion.
(6), review of main view
Main view is where dimensions are concentrated in the drawing. Confirm tolerances on both sides and tolerance on the side of sheet, and mark more stringent ones.
(7) Review of other views. Same method as above
(8) Review of necessary type of force
Molten resin produces a considerable injection pressure on mold parting surface when injected. If maximum type of force of injection machine is less than injection pressure, a gap will occur between templates, and an overflow phenomenon will occur. Calculation of necessary type of force is as follows:
F=P×A
F: Necessary type of force (Kg)
P: injection pressure (Kg/cm2), take 300 to 500, depending on molding conditions
A: projected area of product in injection direction cm2
(9) Review of necessary injection volume
When selecting injection machine, a review of injection volume is required.
Total volume including chat and product is less than 1/2 to 2/3 of maximum injection volume of injection machine.
(10), other matters
If information provided by customer is incomplete, you need to contact customer to obtain all information.
Use a marker to mark what you think is more important for next step.

 

General process of injection mold design work:
Initial review → Basic drawing design of molding products → Mold structure design → Part drawing design → Inspection drawing → Drawing
Design of plastic injection mold starts with design of basic drawing of molded product, and its correctness determines quality of molded product.
Following is a description of design method of basic drawing of molded product:

The most critical is quality of flow and shrinkage rate.

Following aspects should be fully considered:
1. Can cavity be completely filled;
2. Location of splicing marks;
3. Occurrence of bubbles;
4. Deformation of molded product;
5. Cutting mark of point gate;
6. Other.
In design work, according to working conditions, following methods are used to analyze and verify:
1. Comparison of similar molds;
2. Calculation of flow ratio (L/T);
3. CAD, CAE

Following principles should be referred to:

1. Try to use plane;

2. Easy to process;

3. No bad type occurs;
4. There is no influence on dividing line on appearance.

Due to shrinkage of plastic after cooling, mold forming method should consider "molding shrinkage rate" as follows: (for a shrinkage rate of 0.2% as an example)
1 Tolerance on both sides: L=25±0.05 → L0=1.02×25=25.5
2 Side tolerances: L=3-0.2 → L0=[(3+2.8)/2]×1.02=2.96
After above method is calculated, following two aspects must be corrected:
1 Correction of moldability on mold making.
2 Even number of odd-numbered methods.

In order to prevent poor release, it is necessary to set draft angle at fixed side core, but it is generally 30' to 3° within tolerance range of molded product.

If necessary, movable side can also be added with draft angle, but generally it is not added. If there is a bad ejection, it can be solved by adding a ejector.

Follow following principles:
1. Ejection area is as large as possible, because small ejector hole is difficult to process.
2. Try to use dome rod, because square top hole is difficult to process (but made with insert dividing line is simpler).
3, Ejector should be placed near core.
4. Minimum thickness of 1mm around ejector hole is guaranteed.

 

After basic drawing of molded product is completed, the most important work can be carried out - design of mold construction drawing. This part of work accounted for 80% of all research work on mold design. Following is specific design process:

1. Confirmation of slider spacing
Size of mold must not exceed distance between sliders, and a safety distance of 20 mm or more is usually required.

2. Minimum thickness confirmation

Thickness of mold is greater than minimum thickness of injection machine.
3. Confirmation of maximum mold opening stroke
4. Confirmation of maximum clamping force
5. Confirmation of theoretical injection capacity
6. Confirmation of diameter of positioning ring (to select positioning ring model)
7. Confirmation of tip shape of nozzle of injection machine (to select model of sprue sleeve)
8. Maximum thickness calculation
T = minimum thickness + maximum mold opening distance - S1-S2-S

For multi-cavity molds, cavity position should be properly arranged so that projection center is completely centered on mold base and flow path is minimized to achieve a balanced feed.

For plastic injection molds, mold base has been standardized. When selecting a mold base, in addition to size specifications, following aspects should be confirmed:
1. Position of guide bush guide sleeve, some guide posts are on fixed side, and some are on movable side. Choose according to your needs.
2. For thickness of each template, it should be confirmed by combining basic drawing of molded product. Generally, it is preferable to make length of non-formed portion of insert about 30 mm.
3. Currently we have FUTABA's standard mold base CAD library, which can be used to quickly generate mold base drawings.

After template thickness is determined, a review of typing action is performed.
1. Mold opening distance between fixed side plate and flow channel plate S1
S1=point sprue sleeve length + sprue sleeve length +10~20
2. Mold opening distance between flow channel plate and fixed side seat plate S2
S2 = pull hook hook length + 3mm safety distance
3, To determine length of stop bolt
L = fixed side profile thickness + S1
4, To determine length of stop bolt head
5, To determine length of support guide column
L=fixed side profile thickness + S1 + runner thickness + S2+ fixed side seat plate thickness
6, To determine length of pull hook
7, To determine flow path ejector device
8. To determine surrounding mechanism of sprue sleeve
9. To make mold layout that naturally falls after molded product is ejected

Adopt RUNNER EJECTING SET (MISUMI City Retail)

During injection, injection machine creates an instantaneous injection pressure at the bottom of movable side plate, causing deformation of template. To prevent this, a support column can be placed in mold base so as not to hinder ejector and force arrangement in vicinity of each cavity.

In order to maintain a constant mold temperature, a cooling water hole must be opened for cooling water.
Size of cooling water hole has little to do with cooling efficiency. Medium-sized molds generally use ф8.5 water holes, and interface uses PT1/8 pipe threads.
Location and number of cooling water holes are closely related to cooling effect. When determining, it should be as close as possible to cavity and quantity as much as possible, but no interference should occur.

In combination with basic drawing of molded product, position of ejector pin should be properly arranged, taking care not to interfere with cooling water hole and support column.

Company uses standard parts from PUNCH.
Sprue sleeve head SR inch is about 1 mm larger than SR inch of injector nozzle.
Opening of sprue bushing is about 0.5mm larger than φ inch method of nozzle of injection machine.
For taper, it is better to use 1° on the side of sheet.

In combination with molding machine, PUNCH retail products are used.

In order to smoothly discharge air in cavity, an exhaust passage is sometimes required. However, it is not considered in general design. If there is a bad exhaust gas in production, it will be solved.

In order to improve accuracy of movement of ejection member, thereby prolonging life of ejector rod and core, and preventing ejector strain from being pulled, ejection guide pillar and ejection guide sleeve can be designed.

Company has established a naming rule for part number of mold, and determines it according to this rule.

At this point, structural design of mold is basically completed.

After structural design is completed, mold part design is performed according to basic drawing of molded product and mold construction drawing, including following contents:
(1) Design parts drawing to be processed.
(2) Drawing of outer member needs to process.
(3) Specification document of purchase item.

(1) Extracting shape of cavity portion from mold structure diagram. X-Y direction is fitted to template, paying attention to tolerances and fits. Z direction can be fixed with screws, hooks or keys.
(2) Forming part shape and inch method
Determine according to basic drawing of molded product, and consider following aspects:
1. Forming product tolerances.
2. Relationship (coordination) with other parts.
3, To facilitate correction of mold.
4. Processing capacity that can be achieved by mechanical processing methods.
5. Processing costs.
6, other.
(3) Cores are matched with cavity parts in the form of hooks, and X-Y direction is strictly controlled by tolerance.
(4), gate design
(5), fixed method
(6), material, hardness decision
Consider following:
1. Shape and precision of molded product maintain function.
2. Surface quality of molded product determines function.
3. Impact resistance, rigidity, strength should be sufficient.
4. Corrosion resistance.
5. Wear resistance.
6. Machining.
7. Mirror characteristics.
8. Thermal conductivity.
9. Heat treatment.
10. Material prices.

Shape and inch method are determined based on basic drawing of molded article.
Choice of materials refers to above.
Movable side core and cavity design are roughly same as fixed side, but more than design content of ejector portion.
At this point, part related to forming in mold part drawing has been completed, and part design of mold structural part is performed below.

It is necessary to carry out inspection after design of parts drawing, which is as important as design work. Finding errors before putting them into production is more costly and energy-intensive than finding them in production or after completion.
Drawing work can be undertaken by designer himself or by a third party. Following principles should be grasped in inspection:
(1) When designing important designs, it is best to do it when you are energetic.
(2) Work for 1 to 2 hours, should rest for 10 to 15 minutes, keep your head clear.
(3) Don't be afraid of failure, gain experience in growth in failure.
(4) Don't start with detailed design. It should start with overall plan, so it is easy to find big principle errors.
(5) Can investigate problems that occur in use of similar molds, and compare with their own design work.
Main contents of drawing work are as follows:

(1) According to core and cavity schedule, there is no missing design part.
(2) Whether number of molds is appropriate.
(3) Is setting of parting surface correct? Do you meet requirements of mold sample book?
(4) Can cavity be completely filled?
(5) Is production cost within budget?
(6) Is production cost of molded product within budget?
(7) Can mold period be completed?
(8) Has reasonable measures been taken to ensure delivery?
(9) Can molded cavity be smoothly taken out?
(10) Can molded core be smoothly removed?
(11) Is there any improper configuration of gates and runners?
(12) Is there any interference in cooling channel?
(13) Support column, ejector, set guide column for interference?
(14) Is calculation of forming shrinkage ratio correct?
(15) Is insert segmentation method correct?
(16) Is design of components that match each other correctly?
(17) Does forming machine meet requirements?
(18) Are other special requirements satisfied?

(1) Is current design correct or not, can there be improvement?
(2) Is expectation of resin flow correct?
(3) Is core and cavity release countermeasure correct or not?
(4) Is design of slider and sliding core correct?
(5) Is tolerance of matching part correct?
(6) Is exhaust passage suitable?
(7) Is fit clearance appropriate?
(8) Is it difficult to assemble?
(9) Is it convenient to disassemble?
(10) Is there any prevention against bleaching?
(11) Is there any interference between components on both sides?

(1) Are there any inconsistencies in size?
(2) Is shape of section correct or not?
(3) Is number of parts correct?
(4) Is material of parts correct?
(5) Does rigidity of profile meet requirements?
(6) Does cavity rigidity and strength meet requirements?
(7) Is gate shape suitable?
(8) Is processing method properly considered?
(9) Is electrode design correct?
(10) Is there any mistake in standard part issuance?
(11) Has customer's official part change been changed?
(12) Has scrap image been replaced?
(13) Is tolerance of the inch method and the surface roughness too strict?
(14) Is machinability appropriate?
We have seen these design aspects, and finally summarize some of characteristics of advanced countries.
Mould manufacturing industry in developed countries such as United States, Japan, and Germany has following characteristics in production and operation:

Most of mould manufacturing companies in Europe and United States are small in scale, and number of employees exceeds 100. Number of mould manufacturing companies is generally 20 to 50. Configuration of all kinds of personnel in enterprise is very streamlined, one is multi-functional, one person has multiple positions.

Most mould suppliers are concerned with demand for various types of molds in automotive, electronics and other industries to determine their product positioning and market positioning. In order to survive and develop in the market competition, each mould manufacturing companies has its own superior technology and products, and all adopt professional production methods. Most mould manufacturing companies in Europe, America and Japan have a group of long-term cooperation mold users, and there are a number of mould manufacturing companies around large mould suppliers.

Mould manufacturing companies in Europe and United States, especially large-scale mould manufacturing companies, have basically realized computer management. From production planning, process development, quality inspection, inventory, statistics, etc., computers are commonly used, and various departments within company can share information through computer networks.

Unlike domestic mould suppliers, which adopts production organization mode of fitter, mould manufacturing companies in Europe and America rely on advanced process equipment and process routes to ensure accuracy and production progress of parts. Advanced technology and management of European and American mould manufacturing companies have made production of large, precise and complex molds, which have played an extremely important role in promoting development of industries such as automobiles, electronics, telecommunications, home appliances, and have also brought good economic benefits to mould suppliers.