MIM vacuum sintering furnace

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Over the past 30 years, metal injection molding (MIM) technology has produced increasingly complex parts and its applications have covered a wide variety of different industries.

With the growing market demand for high-quality parts with low geometric deformation and strong material properties, the MIM process has been diffused and integrated into production lines in various industries, such as automotive, medical device and mobile phone manufacturing. Fields of high power density, such as modern automotive engines, powertrains and machine building, require small and compact mechanical systems because they offer greater innovation potential and higher productivity. In addition, complex MIM parts have many advantages, such as reducing the assembly time of mass-produced products such as laptops and mobile phones.

In order to meet the industry’s evolving needs for technical requirements and related specifications, we must explore the growth potential of MIM process equipment in terms of accuracy and efficiency. Currently, restrictions on mechanical and chemical properties and optical appearance of parts are mainly caused by the following aspects:

1) Uneven shrinkage (geometric deformation)

Density fluctuation due to uneven mixing of powder and raw material injection and/or first debinding stage; uneven temperature in the sintering furnace.

2) Chemical decomposition and discoloration

Inaccurate process gas management; binder redeposition in the second debinding step; residual sintering furnace contamination.

In addition to these technical constraints, a highly competitive market environment shifts cost pressures to component manufacturers. That’s why more profitable and technologically advanced production equipment and materials are critical in order to move the MIM industry forward.

In addition to the high cost of purchasing raw materials (eg: fine-grained metal powders, polymer binders and ready-made injection materials), high temperature sintering is one of the main cost drivers in MIM processes. The investment and operating costs of debinding sintering furnaces are key to the competitiveness of MIM parts producers. In addition, choosing the most suitable furnace type according to the specific production situation is a prerequisite for success in the MIM industry.

MIM furnace type

Most of the sintering furnaces on the market can be divided into periodic vacuum furnaces and continuous atmosphere furnaces. Brown parts after injection moulding and catalysis/degreasing contain residual polymer, and both furnace types offer options for thermal polymer removal.

On the one hand, if it is to mass-produce relatively large parts that are completely consistent or similar in shape, it is more appropriate to make full use of continuous atmosphere furnaces. In this case, short cycle times and high sintering capacity can lead to favorable cost-benefit ratios. However, in small and medium-scale production lines, this kind of continuous atmosphere furnace with a minimum annual output of 150-200t, high input cost and large volume is not economical. Also, continuous atmosphere furnaces require longer downtime for maintenance, reducing production flexibility.

Advantages of vacuum furnaces

The periodic vacuum sintering furnace has outstanding degreasing sintering process control technology, including the geometric deformation and chemical decomposition of MIM parts finished products can be effectively solved. The solution is to use a sophisticated gas control system, laminar flow of process gas to wash away the volatilized bonding material. In addition, by reducing the hot zone capacity, the temperature uniformity of the vacuum furnace is very good, up to ±1K. Overall, the vacuum furnace’s good atmosphere cleanliness, process parameter adjustability, and low part oscillations make it the technology of choice for producing high-quality parts such as medical devices. The low investment and high cycle flexibility of vacuum sintering furnaces will benefit many companies facing fluctuating order status and the need to produce parts in different shapes and materials. Running a group of vacuum furnaces not only provides redundant production lines, but also allows different process programs to be run simultaneously.

However, some professional vacuum sintering furnaces with the above technical advantages are limited by the small available capacity. Their disadvantage in input-to-output ratio and lower energy utilization, the cost of sintering the part may offset the cost savings in other MIM process steps.

MIM industry requirements for vacuum furnaces

An important factor in the cost-effective operation of vacuum sintering furnaces is the economical process gas and power consumption. Depending on the gas type, these two cost elements of the sintering process can account for up to 50% of the total cost. In order to save gas consumption, an adjustable gas partial pressure mode must be implemented while keeping the debinding and sintering processes free of contamination. To reduce power consumption, create hot zones with optimized heating elements to reduce heat loss. To achieve these design points and keep development costs within a reasonable range, a modern resource-saving vacuum sintering furnace uses fluid dynamics calculation tools to find the optimal airflow and heat flow patterns.

Depending on the weight of the sintered part and the residual polymer content, the binder can build up on peripheral components (eg: exhaust pipes, pumps and hot zones) to varying degrees, resulting in long downtimes for manual cleaning and routine maintain. If the net weight of the material is 400kg (furnace volume >1000L) and the binder content is 3%~4%, then up to 15kg of polymer will be removed in the degassing stage. Even so, most of the exhaust gas (>95%) should be collected at a specific condensation point (such as a binder trap or wax separator). Door-to-door cycle time will increase by over 2 hours due to decontamination and manual cleaning. As such, an inefficient, poorly designed vacuum sintering furnace will reduce operational performance by 15%. MIM manufacturers consider more advanced equipment with automatic cycle cleaning systems to reduce maintenance and keep unplanned failures low.

Equipment selection: The RVS vacuum sintering furnace provided by SIMUWU is an excellent product for processing MIM process. It has good temperature uniformity, high temperature control accuracy, and is equipped with a perfect degreasing collection system to reduce the maintenance cost of the furnace. SIMUWU also provides a professional team of engineers who can solve various problems encountered in the production process and are committed to giving customers the most convenient and efficient experience.