The most important component of automotive molds is cover mold. This type of mold is mainly a cold stamping mold. In a broad sense, "automotive mold" is a general term for molds that manufacture all parts of a car. For example, stamping molds, injection molds, forging molds, casting wax molds, glass molds, etc.
Following mainly analyzes automotive injection mold design and mold concepts:

 

 

Main molding processes and molds for automotive interior products

 

Basic mold structure

 

Injection mold: Names of mold parts

 

1. Upper base plate, 2. Runner plate, 3. A plate, 4. B plate, 5. Mold foot, 6. Ejector panel, 7. Ejector base plate, 8. Lower base plate, 9. Hanging module, 10. Hot runner electrical interface, 11. Timing controller, 12. Positioning ring, 13. Hot runner needle valve oil interface, 14. Water collecting block, 14. Support foot, 15. Ejector oil cylinder, 17. Parallel block, 18. Water joint

 

19, guide column, 20, parallel block, 21, precision positioning, 22, wear-resistant block, 23, female mold insert, 24, support foot, 25, code mold U-shaped groove, 26, return pin, 27, lifter, 28, top block, 29, male mold insert, 30, main lifting ring hole, 31, auxiliary lifting ring hole, 32, ejector pin

 

33, guide sleeve 34, water channel, 35, middle bracket 36, lifter guide slide block 37, support column 38, lifter slide foot, 39, sleeve fixing block 40, ejector pin 41, cylinder limit strip 42, secondary ejection mechanism
Lifter molding structure for interior products
Lifter of larger products (maximum product size greater than 400mm) generally adopts type shown on the right. For specific parameters, see drawing description. Generally, ejection space of lifter is greater than or equal to 65mm.

 

Angle of lifter is generally between 3° and 12°. If it exceeds 12° or there is an angle between ejector ejection direction and parting surface, it is necessary to add an inclined guide pin to ejector plate.

 

Lifter type
Split lifter,
Two lifters are ejected in opposite directions, so possibility of interference between lifter rods is relatively high; lifter distance on parting surface is required to be relatively large, W=tanX*H*2. If distance is too small, a staggered lifter can be used, lifter rods are weakened, and design is staggered.

 

Deformed lifter
In order to increase ejection slope, lifter seat is given an additional slope to increase ejection degree and demoulding slope. A sliding mechanism is made at the joint to deform two-way demoulding structure.

 

Higher pitched lifter,
Lifter does not require much demoulding, and mold is high, lifter is very long, and this lifter structure is used when strength is insufficient

 

Special variant lifter:
This type of lifter structure is rarely used unless it is absolutely necessary. It can solve problem of undercut in direction of lifter ejection.

 

Two-stage lifter
When ejecting, ejector pin pushes bottom of lifter to eject mold. However, when returning to original position, ejector pin does not have a pull-to-reset function. Lifter hits parting surface of front mold to reset.

 

Front mold lifter:
Lifter moves with female mold, but if female mold does not move when inserted, lifter will move backwards under action of guide groove.

 

 

1, straight top block 2, lifter block, 3, secondary top plate 4, oil cylinder
Upper trim water retaining strip mold structure plan

 

 

Water retaining strip exceeds undercut part, and can only be welded, otherwise there will be problems with product demoulding.

 

Key points of problem:
1: Disconnect undercut part and separate lifter to make room for demolding:
2: Try not to eject lifter in one direction, otherwise product will be stuck to lifter.
3: There should be enough space for ejecting lifter.
4: Reduce size of A as much as possible and strengthen back as much as possible

 

 

 

Basic gate forms

 

Basic waterway forms

 

 Slider design considerations
Slider mechanism
Slider is a mold structure created to solve problem of undercut. Basic principle is to convert vertical motion of mold in Z direction into motion in other directions. Because position and direction of undercut direction are inconsistent, various slider structures have evolved. Here we only give a brief introduction. Following figure shows basic structure of slider:

 

During operation of slider, each part is worn due to long-term movement, so surface nitriding treatment is required.

 

 

 

Types of slider mechanisms
Slider mechanisms commonly used at present are: inclined guide column slider and shift block slider.

 

 

Theoretically, two oblique guide pillars are required when slider length is greater than 60mm. But in fact, when we design, we usually use two oblique guide pillars when slider length is greater than 100 to 120.

 

When there are many small sliders on product, making a slider group can greatly reduce processing time and mold complexity.

 

 

Ribs under mesh should be as thick as possible to facilitate glue flow.

 

Change in mesh parameters and whether it is split or not cause a big difference in mold cost

 

Causes of shrinkage:

 

1: Due to excessive wall thickness of ribs and columns, see Figure 1 and Figure 2. (PP generally does not exceed 1/3 of product wall thickness, and ABS generally does not exceed 1/2 of product wall thickness.)
2: Uneven product wall thickness, see Figure 3.
3: Intersection is too thick, see Figure 4 and Figure 5
4: Plane is disconnected because pressure is not enough and plane is more likely to find shrinkage problems (see Figure 6)
5: Gate size is not suitable and injection molding process is too long, resulting in insufficient pressure and pressure holding (insufficient pressure, short shot, insufficient pressure holding, gate is too small, resulting in rapid cooling of gate, and pressure holding cannot enter.
The best solution: Try to thin ribs that cause shrinkage while ensuring product assembly and strength, but at the same time do not affect processing of mold.
Backup plan
One: Solve it through mold structure, through lifter, crater, glue addition, glue reduction, connection and other solutions;
Two: Solve it by adding feed nails;
Three: Solve it through the process.
CAIP requires all mold suppliers to design molds. If there is no assembly requirement on thickness, wall thickness of all buckle seats and B-side contact parts shall not exceed 0.8mm, but B0SS and RIBE with assembly requirements cannot be thinned according to material after making volcanoes or adding glue locally, and ribs shall not exceed 1mm.
Solution to shrinkage
1. Shrinkage caused by excessive wall thickness of ribs and columns can be solved in the mold design by following ways
1. Shrinkage caused by excessive wall thickness of ribs and pillars. Try to reduce ribs on the back to reduce shrinkage, but if rib thickness is less than 1mm, there will be difficulties in mold processing. If boss wall thickness is less than 1mm, wall thickness of push tube will be too thin, easy to break, and mold life cannot be guaranteed:
A. Electrodes with rib thickness less than 1mm are difficult to process. Wire cutting or CNC processing will cause electrode to deform and bend:
B. Electrodes with a thickness less than 1mm are prone to deformation due to heat during EDM processing, and loss is also very serious, which will lead to poor mold processing;
C. If rib thickness is less than 1mm, product filling is also difficult, but demolding is prone to rib breakage.
Considering above points comprehensively, a rib thickness of about 1mm is more economical and more effective in solving shrinkage problem. From our experience, if plastic material is not very ideal, more than 95% of ribs will not produce unacceptable shrinkage on the surface. We have also communicated with many well-known mold companies. Shrinkage cannot be completely eliminated. It can only be reduced to an acceptable range through comprehensive treatment by various means.
In some places (where there is design space) where ribs cannot be thinned, following options are available during mold design process to minimize shrinkage.

 

2: Surface shrinkage caused by uneven product wall thickness

 

1: It is best to solve it by reducing glue on the front or back, but be careful that product cannot have sharp corners to prevent stress concentration. Use ribs to meet product assembly and strength requirements while reducing shrinkage.
2: Reduce shrinkage by uniform transition or reducing glue on the back.
3: Caused by excessive thickness at intersection

 

1: Solve it by reducing glue locally, hollowing out locally, or using a lifter.
In plastic design, a cross structure is the best because it can cope with many different load arrangement changes. A properly designed cross structure that can withstand expected stress can ensure that stress is evenly distributed throughout product. Nodes formed at intersection of cross represent accumulation of material, but center of node can be hollowed out to prevent problems. It must also be noted that material accumulation does not form where intersection and edge of component intersect (Figure 6).
Four: Setting appropriate number of gates, reasonably distributed gate positions, reasonable design of gate size and type, and strengthening ejection are also ways to solve shrinkage.
Five: Solve it through molding process,
Increase injection pressure, increase holding pressure and holding time, and increase cooling time, but injection molding cost will increase.
Six: Solve it by manufacturing high-end molds and improving ratio of plastic materials,
A, 3D water channel hot and cold molding method, can completely solve weld mark, and can effectively improve shrinkage. At present, only Japan can manufacture such molds. Mold is expensive, maintenance cost is high, equipment needs to be updated, and technology is not popular;
B, mold adds a spring pin structure, mold is complex, and debugging is difficult. At present, only GE Polymer Processing Research Center (PPDC) has done such an experiment. It can be used on relatively simple molds. It can only solve a small amount of local shrinkage, and technology is not popular;
C, adding foaming agent to material will affect surface quality and other properties of product;
D, make a gas-assisted mold, and add an appropriate airway structure to B side of product, and tooling cost and injection molding cost will increase.
A side reduces straight surface
It is best to use arcs or curved surfaces instead of flat surfaces to smooth all surfaces, as shown by arrows. Two photos on right are photos of speaker covers of B21 door panels and T11 door panels. A surface of decorative ring of B21 speaker cover is flat, and effect after electroplating is very similar to a miniature print; decorative edges around T11 speaker cover are flat, and effect after product is made is not very full, which looks a bit like a defect.

 

B21 coat rack injection molding
B12 coat rack injection molding