1. Common shrinkage rates of plastic materials?
Answer: ABS, PC, PMMA, PS, PA66+30GF: 1..005
POM, PVC, PE: 1.020
PP, PET, PBT: 1.015-1.020
2. Common defects in plastic parts?
Answer: Glue deficiency, cloak, bubbles, shrinkage, weld marks, black spots, bubbles, stripes, warping, delamination, peeling, etc.;
3. Commonly used plastic mold steel?
Answer: 718, 738, S136, NAK80, SKH51, SKD61, 2344, 8407, 1.2344, H13, etc.
4. What kind of steel is used for high mirror polishing?
Answer: Commonly used high-hardness heat-treated steel, such as SKD61, 8407, S136, etc.
5. What is 2D? What is 3D?
Answer: 2D refers to a two-dimensional plane, and 3D refers to a three-dimensional space. In mold part, 2D usually refers to a plane drawing, that is, a CAD drawing; 3D usually refers to a stereogram, that is, a drawing file of PRO/E, UG or other 3D software.
6. What is default accuracy of UG?
Answer: Default accuracy of UG is 0.0254MM;
7. What is a punch-through? What is a plug-through?
Answer: Male and female mold fitting surface parallel to PL surface is called punch-through surface; male and female mold fitting surface not parallel to PL surface is called plug-through surface;
8. What is relationship between strips and wires?
Answer: Strips and wires are both length units. Strips are Taiwanese terms, 1 strip = 0.01MM; wires are Hong Kong terms, 1 wire = 0.01MM, so 1 strip = 1 wire;
9. What is pillow position?
Answer: Edges of shell plastic parts often have gaps for installing various accessories. Pillow-shaped parting part formed here is called pillow position;
10. What is a crater?
Answer: Shape similar to a volcanic eruption reflected on mold by glue reduction part at root of BOSS column is called a mold crater. It is also often done on deep bone positions to prevent shrinkage;
11. What does "ha" mean?
A: He is mold core, a common term in Hong Kong, and "Xianhe" means "Xian mold core".
12. What is tiger's mouth?
A: Tiger's mouth, also known as tube position, is part used for limiting. It is often used on four corners of mold core to play a role in precise positioning of front and rear mold cores. It is often processed by CNC or mold bed.
13. What is layout?
A: Product layout on mold is called layout. It is often determined by glue injection pattern, mold structure and product itself.
14. What is glue position?
A: Cavity of product on mold is called glue position. That is, plastic part you need;
15. What is bone position?
A: Ribs on product are called bone position. They are mostly used for connection or limiting;
16. What is column position?
A: BOSS column on product is called column position. It is often used for screwing or positioning.
17. What is virtual position?
A: Gap on mold is called virtual position. It is also called avoidance position, which is often used in non-sealing positions.
18. What is a buckle position?
Answer: Hook used to connect product is called a buckle position. Generally, a lifter or a sliding position structure is required.
19. What is a spark pattern?
Answer: Pattern left after EDM is called a spark pattern. Thickness is determined by amount of discharge.
20. What is a PL surface?
Answer: PL is abbreviation of Parting Panel, PL is also called parting surface, which refers to part where male and female molds are in contact when mold is closed.

 

21. What is a computer gong?
Answer: A general name for CNC milling machines and machining centers;
22. What is copper work?
Answer: EDM usually uses easy-to-process copper materials as discharge electrodes, which are called copper work, also known as electrodes. Copper work is generally divided into rough work, rough fine work, and fine work.
23. What is discharge machining?
Answer: EDM is a self-excited discharge. There is a high voltage between the two electrodes of spark discharge before discharge. When the two electrodes are close, medium between them is broken down, and spark discharge occurs immediately. With breakdown process, resistance between the two electrodes decreases sharply, and voltage between the two electrodes also decreases sharply. Spark channel must be extinguished in time after a short period of time (usually 10-7-10-3s) to maintain "cold pole" characteristics of spark discharge (that is, heat energy converted by channel energy cannot be transmitted to depth of electrode in time), so that channel energy acts on a very small range. Effect of channel energy can cause local corrosion of electrode. Method of using corrosion phenomenon generated during spark discharge to process size of material is called electric spark machining.
24. What is spark position usually?
Answer: During discharge process, discharge gap between copper and steel materials is called spark position. Rough spark position is generally 20 to 30, and fine spark position is generally 5 to 15;
25. What is material level?
Answer: Wall thickness of plastic product is also called thickness of wall.
26. What is original body retention?
Answer: Original body retention is relative to cut insert. Original body retention refers to processing of a whole piece of steel material, using iron removal method.
27. What is a weld mark?
Answer: Line formed by meeting of two strands of plastic is called a weld mark. It often appears when multiple points are injected.
28. What is a jet?
Answer: Curved and folded snake-like flow mark formed after plastic enters cavity from injection port is called a jet. Generally, there is an obvious white mark.
29. What does LKM mean?
Answer: LKM refers to LKM mold base. Commonly used mold bases include LKM, Fudeba, Mingli, etc.
30. What does DME mean? What does HASCO mean?
Answer: DME and LKM are both standards for standard parts. DME is American-made and HSACO is European-made. These are standards for export molds;
31. What is undercut?
Answer: Part of product that cannot be directly demolded by male and female molds is called undercut. Generally, it is also a part that needs to be structured.
32. What is foolproofing?
Answer: Foolproofing is an idiom, which means preventing very simple mistakes and preventing daze! For example: an insert has same size of hanging platforms on the top and bottom sides. During on-site assembly, it is very likely that top and bottom sides will be installed upside down, but only one side of insert will be made with a hanging platform. At this time, if top and bottom sides are installed upside down, they cannot be installed. It is impossible to install them wrongly. This action to prevent daze and errors is called foolproofing.
33. What is a molding machine?
Answer: Molding machine is a local idiom, which is what we often call injection molding machine and molding machine.
34. What is a stopper?
Answer: Stopper is art line of clamping mouth, also known as ugly line. It is mainly for front and rear shell materials that are of different sizes and assembled misaligned.
35. What is a flying mold?
Answer: A flying mold is a matching mold. Processing is often not in place, and at this time, fitter needs to make corrections based on experience
36. What is a light knife?
Answer: Action of CNC finishing is called a light knife, which means that processing is in place on basis of roughing.
37. What is frame opening?
Answer: Processing position of mold core on mold base is called frame opening.
38. What is lettering?
Answer: Lettering is a processing method that makes film and then adds font, which is an etching method.
39. What is reverse?
Answer: Method of reversing front and rear mold positions under normal circumstances is called reverse. For example, when a toy car mold is opened, if outer surface of car is placed in rear mold, it is reversed. It is also commonly known as an inverted mold.
40. What is floating?
Answer: Method of ejecting mold with a small insert in a local undercut is called floating. Insert and product will move together for a distance;
41. What is eating front mold?
Answer: When opening mold, product is left in the front mold, which is called eating front mold. That is, front mold is sticky. This situation is quite troublesome and a taboo in mold setting, which often leads to mold scrapping.
42. What is top white?
Answer: Demoulding force required for ejection is large, and ejector is not strong enough, so that product is partially damaged. From the front of product, there is obvious white or glue position is high, which is called top white, also called top high water outlet. This situation will also occur if ejection is unbalanced.
43. What is baking mark?
Answer: Trace left on the surface of product by water entry point during diving is called baking mark.
44. What is code?
Answer: Code is a clamping tool that fixes mold on injection molding machine.
45. What is overcutting?
Answer: Overcutting refers to excessive cutting, that is, when processing workpiece, parts that do not need to be processed are also processed. It is understood as cutting too much.
46. What is a glue cup?
Answer: Inner position of front mold pops up to open mold. It is also a common Harvard position, and front mold pops up.
47. What is a thread cutter?
Answer: Tapping, tapping. Cantonese idiom.
48. What is a beer handle?
Answer: Draft angle is called a beer handle, a Cantonese idiom.
49. When is a two-color mold needed?
Answer: When a product contains two different materials or different colors of same material, a two-color mold is designed for molding!

 

50. What are reasons for insufficient filling of product?
1. Insufficient injection pressure 2. Small glue port 3. Poor exhaust 4. Low mold temperature.
51. Several ways of demolding?
Answer: Smooth release and forced release.
52. What are common ways of glue injection, what are their advantages and disadvantages?
Large water outlet - Advantages: easy processing, easy separation, disadvantages: troublesome processing after removal, large pressure loss.
Bottom glue injection - Advantages: no obvious marks on the side, disadvantages: need to be cut off.
Submersible glue injection - production can be separated automatically, disadvantages: large pressure loss.
Point-in glue - glue mouth left on the surface of plastic part is not obvious, disadvantages: large pressure loss and high cost.
53. What are forms of flow channels?
Answer: There are circular flow channels, trapezoidal flow channels, U-shaped flow channels, etc.
54. What is role of spring?
Answer: Source of force can be mold opening force of mold, but it can be mold closing force of mold.
55. Why does mold need to be demolded?
Answer: To prevent product from being pulled and burred during demolding, forming white marks, and affecting appearance.
56. Role of screws and determination of matching length?
Answer: Screws can only play a tightening role. Effective length is generally 1.5 to 2 times diameter of screw.
57. Role of cold well?
Answer: Role of cold well is to store small part of plastic material with a relatively low temperature that enters mold first, so as to avoid rushing into cavity and affecting quality of plastic part.
58. Role of positioning ring?
Answer: Function of locating ring is to ensure correct relative position between mold and injection molding machine. Generally, negative tolerance is taken, which is less than 0.2;
59. Types of fit?
Answer: Fit is mainly divided into three categories: clearance fit, transition fit, and interference fit.
60. What is function of insert?
Answer: Convenient processing, prevent carbon deposition, facilitate polishing, save materials, help exhaust, easy replacement, and mold repair.
61. What are hardness indicators?
Answer: Hardness indicates ability of a material to resist hard objects pressing into its surface. Commonly used hardness indicators include Brinell hardness, Rockwell hardness, and Vickers hardness. The most commonly used is Rockwell hardness HRC.
62. What is difference between the first angle method and third angle method?
Answer: Method of drawing a projection view by placing an object in the first quadrant with relationship of "viewpoint (observer)" → "object" → "projection surface" is called the first angle method. It is also called the first quadrant method.
Method of drawing a projection view by placing an object in third quadrant with relationship of "viewpoint (observer)" → "projection surface" → "object" is called third angle method. It is also called third quadrant method.
Difference between first angle method and third angle method is position of view;
First angle method: left view is placed on the right, right view is placed on the left, top view is placed on the bottom, and so on;
Third angle method: left view is placed on the left, right view is placed on the right, top view is placed on the top, and so on.
63. How many ways are there to transport water?
Answer: Common ones include straight-through, wrap-around, water tower, spiral, etc.
64. What are basic principles of three views?
Answer: Basic principles of three views are that length is aligned, height is flush, and width is equal.
65. What are categories of injection molding machines?
Answer: According to shape, there are vertical and horizontal types (this is the most common); according to injection volume, there are ultra-small injection molding machines, small injection molding machines, medium-sized injection molding machines, large injection molding machines, and ultra-large injection molding machines. That is, injection volume ranges from a few milligrams to tens of kilograms; according to clamping force, there are: a few tons to thousands of tons.
66. What is appropriate wall thickness of commonly used plastics?
Answer: Appropriate wall thickness of ABS is 1.8-3mm; appropriate wall thickness of PC is 2-3.5mm; appropriate wall thickness of PA is 2-3.5mm; appropriate wall thickness of POM is 1.5-2.5mm; appropriate wall thickness of NORYL is 2-3.5mm.
67. What is overflow value?
Answer: Overflow value refers to value of gap at which plastic product will overflow (that is, burr). Overflow value of ABS is 0.04mm; overflow value of PC is 0.06mm; overflow value of PA is 0.015mm; appropriate wall thickness of POM is 0.04mm, overflow value of PBT+15%GR is 0.03mm; overflow value of PBT+30GR% is 0.02mm; overflow value of PMMO is 0.065mm; overflow value of PVC is 0.07mm; overflow value of AS is 0.05mm; overflow value of PS is 0.05 mm; overflow value of PP is 0.03mm; overflow value of PE is 0.02mm.
68. How big is standard drawing frame?
Answer: Commonly used drawing frames are A0, A1, A2, A3, and A4. Size of A0 frame is 1188MM*840MM, size of A1 frame is 840MM*594MM, size of A2 frame is 594MM*420MM, size of A3 frame is 420MM-297MM, and size of A4 frame is 297MM*210MM.
69. Classification of mold sizes.
Answer: Each company has different standards for classifying mold sizes, but common classification standards are as follows: molds of 15~30 series mold bases are classified as small molds; 30~50 series mold bases are classified as medium molds; molds of mold bases above 50 are classified as large molds.
70. What is elastic deformation? What is plastic deformation?
Answer: When an object is deformed under action of external force, when external force disappears, object can return to deformation before deformation, which is called elastic deformation; when external force disappears, object cannot return to deformation before deformation, which is called plastic deformation.
71. What materials are commonly used for mold bases?
A: Mold base is usually made of King Steel (Hong Kong name), which is medium carbon steel and 45# steel.
72. What is role of water transportation?
Answer: Function of water transportation is to control temperature of mold core. Commonly used frozen water, room temperature water, and oil temperature.
73. Classification of molds?
Answer: Molds can generally be divided into plastic molds and non-plastic molds. Non-plastic molds include: casting molds, forging molds, stamping molds, die-casting molds, etc. Plastic molds are divided into: injection molding molds, blow molding molds, compression molding molds, transfer molding molds, extrusion molding molds, thermoforming molds, rotational molding molds, etc. according to production process and production products. According to different types of pouring systems, molds can be divided into three categories: large water mouth molds, fine water mouth molds, and hot runner molds.
74. What is a venting groove? What is function of air discharging groove?
Answer: Groove used for exhaust on broken surface or scratched surface of mold core is called a venting groove. Venting groove has two main functions: one is to remove air in mold cavity when injecting molten material; the other is to remove various gases generated by material during heating process.
 
75. What is a pouring system?
Answer: Plastic flow channel from injection machine nozzle to cavity is called pouring system. Pouring system includes main channel, branch channel, gate and cold well.
76. Advantages and disadvantages of hot nozzles.
Answer: Advantages: 1. No gate material, no need for post-processing, making the entire molding process fully automated, saving working time and improving work efficiency. 2. Small pressure loss. 3. Reuse of gate material will degrade performance of plastics, while use of hot runner system without gate material can reduce loss of raw materials, thereby reducing product costs. 4. Hot nozzle adopts standardized and serialized design, equipped with a variety of optional nozzle heads, and has good interchangeability.
Disadvantages: 1. The overall mold closing height is increased, and the overall height of mold is increased due to addition of hot runner plates. 2. Heat radiation is difficult to control. The biggest problem of hot runners is heat loss of runner, which is a major issue that needs to be solved. 3. There is thermal expansion, thermal expansion and contraction are issues we need to consider when designing. 4. Cost of mold manufacturing has increased, and price of standard accessories for hot runner systems is relatively high, which affects popularity of hot runner molds.
77. Who will participate in product review?
Internal review: mold designer, mold maker, design supervisor, mold engineer, mold supervisor
Review with customers: product designer, design supervisor, mold supervisor, mold engineer, mold designer
78. How to compile BOM table and mold material list?
It consists of 1. No. 2. Name 3. Specification 4. Quantity 5. Material 6. Remarks. When compiling, compile main steel materials first and compile in order
79. How to solve problem of product sticking to slider?
1. Increase demolding slope 2. Slide mold saving, 3. Make a mechanism ejector inside slider.
80. For example, for a set of mobile phone molds, how long does it take to complete 2D and 3D? How long does processing cycle take?
2D structure drawing 3-4 days, 3D mold splitting 2 days, loose parts need 1-2 days, processing cycle is about 25 days
81. Have you ever made a large mold? How big is it? What should be paid attention to?
Large mold I have made is 1 meter high. Pay attention to: 1. Mold parallelism 2. Water transportation processing 3. Inner mold material frame 4. Front and rear mold guide
82. How big is M16 screw cup head?
24MM
83. What are heat treatment methods for steel?
1. Nitriding 2. Annealing 3. Quenching
84. Please list common mold structures, at least 5 types
1. Slider 2. Lifter 3. Front mold slider 4. Front mold lifter 5. Front mold core pulling 6. Back mold core pulling 7. Secondary ejection 8. Inner slider
85. What issues should be paid attention to in design of transparent product molds
1. Mold steel must first use steel with better polishing performance, such as NAK80, S136, etc.
2. Avoid entry of glue point design, find a side glue port, and design flow channel into an arc with a certain curvature to reduce injection speed. Port is generally a fan-shaped glue port
3. Do not set ejector pin at the end of product
4. Side should have a larger draft angle
5. Where there is a buckle, try to use an external inclined ejector
86. Commonly used standards Z40, Z01, BP20, and BP40 for outlet mold represent meaning.
Generally DME or HASCO, Z40 represents ejector pin, Z01 represents guide pin, BP20 represents water plug NPT1/4, and BP40 represents water plug NPT3/8.
87. What is difference in degree between inclined guide pin of slider and inclined pressure block? Why?
Difference of 2~3 degrees is to prevent mutual interference during mold opening, which will cause slide position to be unable to retreat.
88. What are general principles for demolding products?
General principles for reducing glue
89. What inner mold materials are generally used for plastics and what are properties of plastics and steel (at least 3 types)
PP/PVC, PMMA—S136, S136H POM—8407 or 2344ABS, AS—NAK80.
 
90. When a set of molds is being tried, what are basic conditions for molding process?
Temperature, pressure, time.
a. Temperature: material temperature (temperature after plastic is melted)
b Pressure: injection pressure
c Time: mold filling and holding time to cooling and setting time
91. Size relationship between nozzle hole ∮A and injection molding machine ∮B is:
∮A>∮B, that is, nozzle hole is generally 1~3mm larger