Metal Injection Molding (MIM) Of Precision Metal Components For The Automotive Segment

car parts
Fig: Applications of Metal Injection MOlding 
     components in an Automotive

Transport plays a very important role in the existence and civilization of the human race. From ages, humans have always looked at options to move faster and quicker than their individual capacity and thus leading to the invention of the wheel, which over the years has been upgraded for use in modern-day hybrid vehicles, which are fast, technology-driven and reliable. The Automobile of the current era has a lot of moving, mechanical parts that provide immense scope for advanced technologies to come up with innovative and cost-effective solutions. One such advanced manufacturing technology is Metal Injection molding (MIM), which has vibrant scope in the automotive segment due to the requirement of complex profiles, special materials, and quick volume ramp-ups.

MIM technology has added advantages with reference to design flexibility, dimensional accuracy, and material performance capabilities for applications in the automotive segment. Engine components such as turbochargers, fuel injectors, automotive access controls and also components for vehicle safety system are few such examples of MIM components used in automotive applications. Complex geometries with close dimensional tolerances along with superior material properties and shape making capabilities drawn from plastic injection molding can be manufactured through Metal Injection Molding . A wide range of materials – from low alloy steels to high-temperature steels and superalloys – that are hard and expensive to machine, can be processed.

Typical applications of MIM components used in an automotive are as shown in Figure 1. MIM components are also used in applications such as lock caps and lock shafts, housings, cams for electric seating and bonnet lock parts. MIM components could potentially replace multiple single engine components made from conventional technologies to an integrated assembly, resulting in significant cost savings.

Selection of the proper material for a particular application is decided based on the functional and technical requirements of the component. Table 1 lists the materials used for applications with their properties.

Material Category

Type

Typical Materials

Typical properties & application

Low alloy steels Low Carbon, Case Hardening 4600 series (Fe-Ni-Mo) Value High toughness & good surface wear resistance

General engineering applications

Med Carbo, Through Hardening 4630-4605 (Fe-Ni-Mo-Cr) High strength General engineering applications
High Carbon, Through Hardening 4680, 52100 High strength & high wear resistance Bearing steel
Stainless steels Austenitic 304L, 316L Column 4 Value 4 Best corrosion resistance, High ductility
watch links, medical devices parts, food processing equipment parts,Medical & dental device, marine components & non-magnetic housings
Martensitic 410, 420, 440A/B/C High strength & wear resistance and medium corrosion resistance
Multi-utility hand tools, mobile phone components
Precipitation hardening 17-4PH Medium strength & wear resistance and good corrosion resistance
Sporting weapons, mobile phone
Components, general engineering applications
Ferritic 430 Good magnetic
properties with medium corrosion resistance
Magnetic probes, sensors, armatures and pole piece
Tool steels Die steels S-7, D-2 High strength & wear resistance
Hydraulic slides, high wear-resistant applications
High-speed steels M-2, T-15, 10-V  High strength & wear resistance
Hydraulic slides, high wear-resistant applications
Non-ferrous Copper Cu + Ni-Sn combinations High thermal and & electrical conductivity
Titanium CP Ti, Ti6Al4V Lightweight, high strength, and best corrosion resistance
Refractory alloys Tungsten base W+ Cu-Ni-Fe combinations High density
Specialty and superalloys Magnetic materials Si-Fe, Fe -49 Co-2V Good Soft magnetic properties
Electronic packaging materials Kovar, Fe-Ni (Invar) Low thermal expansion

Following examples show how MIM has effectively introduced value addition and value engineering in few of the critical automotive applications.

 1. Proportional Valves in Off-high way Vehicles:

Catcher, tension bar, new base cap & body—. These automotive components are used in proportional valves found in hydraulic circuits of off-highway and farm equipment. The two parts forming the new base and body are made of MIM 17-4 PH stainless steel, while the catcher and tension bar are formed of 4605 low-alloy steel. These parts were formerly produced via machining, welding, conventional PM, and fastening. The conventional manufacturing method led to multiple operations, resulting in increase in the lead time for manufacturing and wastage of raw material. All dimensions of the two parts forming the new base are achieved in the as-MIM condition, including the internal thread in the body. The catcher receives a grinding and burnishing operation to attain the OD tolerance and surface finish, while the tension bar needs no secondary operations. The external threads are also achieved as MIM. Heat-treated properties include a minimum density of 7.5 g/cm³, 1,550 MPa ultimate tensile strength, yield strength of 1,400 MPa, 3% elongation, and 42–48 HRC hardness range. By completely re-designing the parts to maximize the advantage offered by Metal Injection Molding, the customer obtained cost savings estimated at 65% of previous manufacturing route, with annual production of 350,000 pieces.

Automotive part
Fig 1: MIM components in proportional valves for off highway vehicles

2. Shock Absorbers:

The steel top plate that goes into shock absorbers of a particular automobile is developed by MIM. The complexity of the part with its 18 holes and six thin ribs connecting to a ring around a central hole presented a challenge to complete filling. The gating and venting system played a key role in producing this part defect free. It is produced close to net shape, with surface grinding to achieve flatness and a facing operation to achieve height tolerance being the only additional secondary operations performed. The material used is MIM 4605 low carbon alloy. After heat treating, the part has a density of 7.5 g/cm³, ultimate tensile strength of 1,550 MPa, yield strength of 1,400 MPa, elongation of 3%, and a hardness range of 42–48 HRC. This application is a new design for MIM and delivers increased repeatability/accuracy of the shock absorber over the previous machined version, with estimated cost savings of 25%.

Automotive part
Fig 2: Steel top Plate – Shock absorber Application

3. Diesel Fuel Pump

The pinion ring that goes into the metering valve in diesel fuel pump is manufactured through MIM. The material used is MIM 8620, which is a low carbon steel. The critical profile with multiple functional features make it an excellent candidate for MIM. This component was previously manufactured through the machining route and had to go through the operations of bar stock machining, slot cutting, gear cutting, chamfering and threading. These multiple machining operations resulted in increased cost and lead time, which was a pain point for the customer as the components were required in large volumes. The entire profile is now produced in MIM without any secondary operation, including the internal thread made possible through the thread inserts used in the molding tool. The following advantages are realized after migration to MIM: 1. higher repeatability 2. reduction in raw material wastage by 60% 3. No machining burrs on functional area 4. Cost savings of 40% MIM as a technology is very adaption friendly and could be applied to any sector with ease.

APG
Fig 3.1: Piston Ring
Automotive part application ring
Fig 3.2: End Application

The challenge is to find the best-fit parts, which can provide value addition compared to any other manufacturing technology. The growing automotive segment seems to offer many such opportunities for MIM. The upcoming EV sector is one such example to have potential applications for MIM, especially in Copper.

Material development inputs by Mr.Sachin Malgave and Mr.Mukund .N (R&D team, INDO-MIM)