In the MIM feeding process, which is better, plastic based or wax based?

In the MIM feeding process, which is better, plastic based or wax based?

Is plastic based binder or wax based binder used in MIM feeding process of metal powder injection? What are the differences between plastic based and wax based adhesives in mixing, injection molding, degreasing and sintering processes? The following is a brief introduction to the differences by ZHONGWEI Precision Editor of Qinhuangdao.

1、 Mixing stage

Wax based binder:

1. The mixing temperature is lower than 120 ℃, and the mixing time is shorter;

2. Sealed mixing, airtight design to reduce wax heating loss;

3. Plastic based mixing equipment can be used, but temperature control shall be paid attention to when the shear force is large.

Plastic based binder:

1. The mixing temperature is higher than 150 ℃, and the softening time is long;

2. Open mixing and kneading;

3. The wax based mixer is not available, and the shear force is insufficient;

4. Special powder mixing shall be protected by adding nitrogen;

5. High shear force can fully soften plastic based rubber.

In general, the wax based binder is mainly paraffin, with low viscosity and easy volatilization; Therefore, it is easy to mix, but it should also be noted that the temperature should not be too high (lower than 120 ℃), and the air tight design can reduce volatilization loss. The plastic based binder is mainly POM, with high viscosity and low volatilization; Mixers with large shear force and higher temperature setting (greater than 150 ℃) are required to reduce the viscosity of the binder; Due to the high temperature and open type, nitrogen protection is required in special cases to prevent some special metal powders from being oxidized.

2、 Injection stage

Wax based binder:

1. Good lubricity, low firing rate can also be achieved, and the hydraulic press can also inject metal powder into MIM;

2. Mold temperature and metal powder injection MIM tube temperature are low;

3. Rapid firing speed is easy to cause obvious shell effect in powder glue separation, which is due to the low viscosity of wax, so it is difficult to save sand hole defects of parts with high polishing brightness.

Plastic based binder:

1. Only when the high-speed motor is used, can the plastic based feeding be done well;

2. The metal powder injection molding machine has high injection speed, high injection pressure and long pressure holding time;

3. Screw compression ratio is very important, screw length should be short;

4. The mold temperature should be high (>120 ℃) to reduce the residual stress of metal powder injection blank;

5. The temperature control of the material pipe should be more strict, and the operation without injection should be cooled immediately to avoid POM cracking!

The injection molding stage is similar to the mixing stage. The high viscosity of the plastic based binder also brings difficulties to the metal powder injection molding. Due to the low viscosity and good lubrication of wax based binder, the metal powder injection molding machine with low pressure, low injection rate and low mold temperature can meet the requirements, but the fast injection rate will easily lead to the separation of powder and glue, resulting in sand hole defects of the final product. For plastic based adhesives, high-speed electric metal powder injection molding machine is required, with short screw, high injection speed, high injection pressure and mold temperature, and long pressure holding time; In addition, the temperature control of the material pipe should be more strict, and the temperature should be lowered immediately without injection to avoid POM cracking!

3、 Degreasing stage

Wax base (dissolution/thermal desorption):

1. The product is easy to deform due to dissolution;

2. The primary removal efficiency is low, the safety of the stripping equipment is poor, and the solvent fire prevention and recovery cause environmental protection and safety problems;

3. The dissolution is suitable for large parts, and the structure should have a supporting plane.

Plastic base (acid catalyzed removal):

1. Fast catalysis, suitable for meat thickness less than 5mm, high efficiency;

2. Simple equipment and high safety;

3. The by-products are all gases (CO2, N2), which are easy to manage.

The above is about the differences between metal powder injection MIM plastic based and wax based binders in the mixing, injection molding, degreasing and sintering processes, which are compiled by Qinhuangdao Zhongwei Precision Small Group. Is it helpful for you to better select binders? If you want to know more about metal powder injection molding technology, please consult the MIM technology professional team of Zhongwei Precision Metal Powder Injection Molding in Qinhuangdao!