Powder metallurgy belongs to green manufacturing technology.Compared to traditionally manufactured parts, these parts exhibit excellent hardness, strength, and toughness. They feature high quality, high efficiency, and low cost, making them widely used in industries such as automotive components, electronics, and aerospace. As industrial and automation standards continue to improve, the requirements for components have become stricter. The issue of burrs has received significant attention, and deburring has become an important processing step.

一. Causes of burrs

1. Mold

Powder metallurgy molds generally consist of four parts. For example, the mold used for

producing compressive strength specimens consists of an upper punch, a lower punch, a mandrel, and a die.

(1) Mold clearance

The filling effect that occurs at the mold clearance is the fundamental cause of burrs.

(2) Precision of the mold

In production practice, the gaps between the punch and the die, as well as between the punch and the mandrel, change dynamically. As a result, the powder particles deform in response to these changes in gap size, leading to work hardening. This process increases the hardness and wear resistance of the powder particles. As wear progresses, the surface roughness of the die decreases, thereby increasing the friction between the powder and the die. This can result in burrs during demolding, or even prevent proper shaping of the material.

3) Damage to the mold

Powder metallurgy parts often have chamfers. To reduce subsequent machining and save costs, the chamfers are incorporated into the mold design. However, this can lead to thin edges or even sharp corners on the mold, which are prone to damage. Due to the complex shape of the molds and the high manufacturing costs, they are typically not replaced unless it affects the final product quality. As a result, burrs and sharp edges may remain. These burrs usually have regular shapes and occur at the locations where there are defects in the mold.

(4) Mold Installation and Use

Mold installation is generally carried out from bottom to top and from the inside out, with positioning relying on the fit between the mold components. Due to the presence of clearance between the mold parts, it’s difficult to ensure uniform distribution of this clearance during installation and adjustment. On the side with larger clearance, burrs are likely to form, while on the side with smaller clearance, dry friction can lead to localized adhesive wear. This is especially problematic when shaping irregularly shaped parts, as misalignment between the mold’s pressure center and the machine tool’s pressure center causes instability. This not only results in large burrs but also accelerates mold wear and damage, thereby affecting the precision of the equipment. All these issues can lead to irregularly shaped burrs in certain areas.

(5). Equipment accuracy

Insufficient equipment precision leads to poor operating conditions of the mold, thereby causing burrs to form. Additionally, if the powder filling level exceeds the device’s range of motion or if the pressing pressure is too high, resulting in insufficient tonnage capacity of the equipment, this can also lead to unstable operation and burr formation. Such burrs typically appear randomly on the surface of the parts.

二、 Machining Equipment  

Metal cutting, in essence, is a process in which metal undergoes deformation due to the force exerted by the cutting tool. During cutting, the metal in the areas of the workpiece’s edges, corners, and ridges undergoes significant plastic deformation. As the metal separates from the surface of the workpiece, some of it remains attached to the edges, corners, and ridges, resulting in burrs.

II. The Impact of Burrs on Product Quality

1. It affects the product’s positioning accuracy. Powder metallurgy typically uses longitudinal pressing, resulting in poor side surface formation of the product. For parts with holes on the sides, machining is often required. The presence of burrs inevitably leads to positioning errors, thereby affecting the precision of hole machining. For parts requiring high precision, burrs must be removed before machining. Additionally, burrs also affect the accuracy of part inspection.

2. It affects the product’s assembly performance. For components with high assembly requirements, burrs can easily cause interference and jamming between mating parts. Examples include motor bushings, guide sleeves in automotive shock absorbers, bottom valve seats, and pistons. The presence of burrs directly impacts the ability to meet assembly specifications.

3. It affects the product’s performance. During mechanical operation, friction causes burrs to break off, thereby accelerating wear and leading to premature failure of components. In hydraulic systems, these broken burrs mix with the hydraulic oil and enter the system’s circuits, disrupting normal operation and causing issues like crawling motion and vibration.

4. It affects the surface quality of the product. Burrs reduce the smoothness of the surface, and in applications where high surface quality is required, this can lead to parts being rejected. For example, some gear pump side plates cannot be used because the burrs have not been removed or have not been properly removed.

5. It affects the heat treatment properties of the product. Parts with burrs are prone to stress concentration during heat treatment, leading to cracks and a decrease in the part’s fatigue strength. This is a critical issue for parts that are subjected to high loads and high-speed motion.

III. Special deburring process (mechanical) for the powder metallurgy industry

1. Planar deburring machine (double-sided automatic flipping)

Wet deburring method is used, with automatic part flipping. Parts are conveyed by a magnetic conveying mechanism. A demagnetizer is installed at the discharge port. During operation, both power heads work simultaneously. Each power head utilizes a fourbrush system that rotates in both clockwise and counterclockwise directions, along with servocontrolled lifting for precise movement. This setup allows for efficient deburring of multiple areas on the surface while creating uniform fillets. The system also features automatic compensation mechanisms. It can be integrated with upstream and downstream processes to enable unmanned production. It’s suitable for deburring parts with a thickness of up to 100 mm and an outer diameter of φ140 mm or less.

Due to the characteristics of their manufacturing process and materials, powder metallurgy parts exhibit significant differences from machined parts in terms of mechanical properties and performance. In addition to continuous improvements in molds, equipment, and processing techniques during production, selecting a suitable and reliable deburring method is also an essential measure.