Mold knowledge

There are many kinds of molds, which can be divided into: according to the processing object and processing technology:

① Mold for processing metal.

② Processing non-metal and powder metallurgy mold. Including plastic molds (such as two-color molds, pressure molds and extrusion molds, etc.), rubber molds and powder metallurgy molds. According to the structural characteristics, the die can be divided into a flat punching die and a cavity die with space. Molds are generally single, small batch production.

Production process:

Mold is a model, according to this model to make products, but how the mold is produced, most of the mold professionals may not answer it. Molds have played an irreplaceable role in our lives, most of our daily necessities can not be separated from molds, such as computers, telephones, fax machines, keyboards, cups, etc. It goes without saying that these plastic products, in addition, like the car and motorcycle engine cover is also made with molds, light a variety of car molds will be used more than 20,000. Therefore, the role of modern life mold is irreplaceable. As long as the mass production is inseparable from the mold.

So how is the mold made?

The following is a simple introduction to the modern mold production process:

Mold Manufacturing:

The requirements of mold design and production are: accurate size, smooth surface; Reasonable structure, high production efficiency, easy automation; Easy to manufacture, high life, low cost; The design conforms to the technological needs and is economical and reasonable.

Mold structure design and parameter selection should consider rigidity, directivity, unloading mechanism, positioning method, gap size and other factors. The wearing parts on the mold should be easily replaced. For plastic molds and die casting molds, it is also necessary to consider the reasonable pouring system, the flow state of molten plastic or metal, and the position and direction of entry into the cavity. In order to improve productivity and reduce runner casting losses, multi-cavity molds can be used to complete multiple identical or different products at the same time in a mold. Molds with high efficiency, high precision and high life should be used in mass production.

Stamping die should use multi-station progressive die, carbide insert progressive die can be used to improve life. In small batch production and trial production of new products, simple molds with simple structure, fast manufacturing and low cost should be used, such as combination dies, sheet dies, polyurethane rubber dies, low melting point alloy dies, zinc alloy dies, superplastic alloy dies, etc. The mold has begun to use computer-aided design (CAD), that is, through a set of computer-centered system to optimize the mold design. This is the development direction of mold design.

According to the structural characteristics of mold manufacturing, it is divided into plane punching die and cavity die with space. The punching die uses the size of the punch die and the die to match accurately, and some even have no gap fit. Other forging die such as cold extrusion die, die casting die, powder metallurgy die, plastic die, rubber die, etc., are cavity die, used to form three-dimensional shape of the workpiece. Cavity die in the long, wide, high three directions have size requirements, the shape is complicated, difficult to manufacture. Mold production is generally single piece, small batch production, manufacturing requirements are strict and accurate, and more precision processing equipment and measuring devices are used.

The surface punching die can be formed by EDM, and then the precision can be further improved by form grinding, coordinate grinding and other methods. Form grinding can be done by optical projection curve grinding machine, or by surface grinding machine with shrink copy, trimming wheel mechanism, or by special form grinding tool on a precision surface grinding machine. The coordinate grinder can be used for precise positioning of the mold to ensure precise aperture and hole spacing. A computer numerical control (CNC) continuous trajectory coordinate grinder can also be used to grind punch and die of any curved shape. Multi-purpose copying milling machine machining, EDM machining and electrochemical machining. The machining quality of the cavity can be improved by the combination of contour milling with NC and the addition of a three-way translational head device in EDM. The production efficiency can be improved by adding gas-filled electrolysis in ECM.

Process performance:

The manufacture of molds generally goes through several processes such as forging, cutting and heat treatment. In order to ensure the manufacturing quality of the mold and reduce the production cost, the material should have good malleability, machinability, hardenability, hardenability and grindability. It should also have a small oxidation, decarburization sensitivity and hardening deformation cracking tendency.

1. Malleability: It has low resistance to hot forging deformation, good plasticity, wide forging temperature range, low tendency of cold cracking and precipitation of mesh carbide.

2. Annealing process: wide temperature range of spheroidizing annealing, low annealing hardness and small fluctuation range, high spheroidizing rate.

3. Machinability: large cutting amount, low tool loss, low machining surface roughness.

4. Oxidation and decarburization sensitivity: When heated at high temperature, the antioxidant capacity is good, the decarburization rate is slow, the heating medium is not sensitive, and the tendency to produce pitting is small.

5. Hardenability: uniform and high surface hardness after quenching.

6. Hardenability: A deeper hardening layer can be obtained after quenching, and the quenching medium can be hardened using a moderate quenching medium.

Seven. Quenching deformation cracking tendency: conventional quenching volume change is small, shape warping, distortion is slight, abnormal deformation tendency is low. Conventional quenching cracking sensitivity is low, insensitive to quenching temperature and workpiece shape.

8. Grantability: The relative loss of the grinding wheel is small, no burn limit grinding amount is large, it is not sensitive to the quality of the grinding wheel and cooling conditions, and it is not easy to wear and grind cracks.

Performance:

1. Low density: Low density of plastic is of great significance for reducing the weight of mechanical equipment and saving energy, especially for vehicles, ships, aircraft and space spacecraft.

2. High specific strength and specific stiffness: the absolute strength of plastic is not as high as metal, but the density of plastic is small, so the specific strength (σb/ρ) and specific stiffness (E/ρ) are quite high. In particular, reinforced plastics made of a variety of high-strength fibrous, flaky and powdered metal or non-metal as fillers have higher specific strength and stiffness than metal.

3. Good chemical stability: the vast majority of plastics have good acid, alkali, salt, water and gas resistance, under general conditions, they do not chemically react with these substances.

4. Electrical insulation, heat insulation, sound performance is good.

5. Good wear resistance and self-lubrication: the friction coefficient of plastic is small, good wear resistance, has a good self-lubrication, plus the specific strength is high, the transmission noise is small, it can work effectively in liquid medium, semi-dry or even dry friction conditions. It can be made into machine parts such as bearings, gears, cams and pulleys, and is very suitable for occasions where the speed is not high and the load is not large.

6. Strong bonding ability.

7. Good forming and coloring performance.

Care and maintenance:

1: The cutting edge of the mold must be ground after long-term use, and the cutting edge surface must be demagnetized after grinding, and it cannot be magnetic, otherwise it is easy to block material. Mold using enterprises to do detailed records, statistics of its use, care (lubrication, cleaning, rust prevention) and damage, according to which can be found which parts, components have been damaged, wear degree, to provide information to find and solve the problem, as well as the mold molding process parameters, product materials used, in order to shorten the mold test time, improve production efficiency. Should be in the injection molding machine, the normal operation of the mold, test the performance of the mold, and the size of the final molding of the plastic parts measured out, through this information can determine the current state of the mold, find out the cavity, core, cooling system and parting surface damage, according to the information provided by the plastic parts, you can judge the damage of the mold and maintenance measures.

2: Spring and other elastic parts in the use of the spring is the most vulnerable to damage, usually fracture and deformation phenomenon. The way to take is to replace, in the replacement process must pay attention to the specifications and models of the spring, the specifications and models of the spring through the color, outer diameter and length three to confirm, only in the case of the same three can be replaced. The spring is of the best quality imported.

3: The punch is prone to break, bend and chew during the use of the mold, and the punch sleeve is generally chewed. Punch and punch sleeve damage are generally replaced with the same specification parts. The parameters of the punch mainly include the size of the working part, the size of the installation part, the length size, etc.

4: Fastening parts, check whether the fastening parts are loose, damaged phenomenon, the way to take is to find the same specification of parts for replacement.

5: Press parts such as press plate, good force glue, etc., discharge parts such as stripper plate, pneumatic jacking, etc. During maintenance, check the relationship between the parts of each part and whether there is damage, repair the damaged part, check whether there is gas leakage phenomenon, and take measures for the specific situation. Replace the air pipe if it is damaged.

Several important parts of the mold should be focused on tracking and testing: The role of ejecting and guiding parts is to ensure the opening and closing movement of the mold and the ejecting of plastic parts. If any part of the mold is stuck due to damage, it will cause production to stop. Therefore, the lubrication of the mold thimble and guide post should be kept regularly (to choose the most suitable lubricant), and the thimble and guide post should be regularly checked for deformation and surface damage.

After the completion of a production cycle, professional anti-rust oil should be applied to the working surface, moving and guiding parts of the mold, especially the protection of the elastic strength of the bearing parts of the gear and rack mold and the spring mold to ensure that they are always in the best working condition;

As the production time continues, the cooling channel is easy to deposit scale, rust, silt and algae, etc., so that the cooling channel section becomes smaller, the cooling channel Narrows, greatly reduces the heat exchange rate between the coolant and the mold, and increases the production cost of the enterprise, so the cleaning of the flow channel should be paid attention to;

For hot runner molds, the maintenance of the heating and control system is conducive to preventing the occurrence of production failures, so it is particularly important.

Cause of loss

1, the main working parts of the mold material problems, improper selection of materials. Material performance is poor, not wear-resistant; Die steel is not refined and has a large number of smelting defects; Convex and concave die, forging forging process is not perfect, there are hidden dangers of heat treatment.

2, mold structure design problems, die structure is unreasonable. The slender punch is not designed to strengthen the device, the discharge port is not smooth, there is stacking, the discharge force is too high, and the punch is subjected to alternating load.

3, the mold making process is not perfect, mainly in the convex and concave die forging billet internal quality is poor, heat treatment technology and process problems, resulting in the convex and concave die quenching opaque, soft points and uneven hardness. Sometimes there are micro-cracks, even cracking, grinding and polishing is not in place, and the surface roughness value is too large.

4, no lubrication or lubrication but the effect is not good.