What is Deburring?
Deburring is a secondary operation of the machining process that improves the final quality of a product by removing raised edges and unwanted chunks of material, known as burrs, left over from the initial machining process . Burrs are produced by shearing, bending, cutting, perforating and compressing material. These occur mainly on soft and malleable materials. Deburring machines are used to remove burrs by mechanical, electrochemical and thermal methods.
Materials deform plastically when shear or bending forces are applied until failure. Areas along the edges become bent, elongated and pinched. These elongations and extrusions occur at the cutting edge, especially at the entry, sides and exit of the tool. Burr formation and size are difficult to predict and quantify. Therefore, the efficiency of deburring is highly empirical and based on multiple production trials before being perfected by the manufacturer.
As mentioned earlier, deburring can be done in a number of ways. Most of these processes are “global” and affect the entire product. There is no control over the point of application of global or general deburring. The deburring process affects the final quality of the product by altering the final dimensions and contaminating the surface with chemical and abrasive residues. Therefore, the deburring process must be carefully selected and controlled to prevent any changes to the desired characteristics of the product.
The importance of deburring
Deburring remains an integral part of the production process for the following reasons:
- Burrs prevent proper assembly and assembly of parts.
- Since the burr is the starting point of failure, the parts are prone to fatigue and cracks.
- Cracks and rough surfaces are prone to corrosion
- Rough edges can pose safety hazards to workers and end users
- Burrs reduce the aesthetic quality of the part
Edge quality has a major impact on a product’s shape, performance and longevity. Burrs and raised edges can interfere with the proper fit and assembly of machine parts. These are critical for precision components used in the aerospace, automotive and electronics industries. In addition to fitting properly, mating parts such as gears, rollers and other sliding surfaces, burrs can strike and damage the part. Fatigue life of products with burrs is significantly reduced compared to parts without burrs. Machining produces residual stresses due to work hardening along sheared and bent edges. These cause changes in the mechanical properties of these areas. Holes, slots, and notches are stress concentration features.
As the burrs have a more irregular profile and are often located on the outermost edges of these features, the burrs can act as crack initiation points.
熱閃光和翻滾閃光會產生裂縫，從而促進局部腐蝕。水、電解質和其他腐蝕性物質會積聚並滯留在縫隙中。如果塗層應用不當，也會發生腐蝕。零件表面凸起區域的塗層可能比齊平表面薄。
Raw edges are also a safety hazard, as sharp edges can pierce pressurized lines and cables. Personnel handling burr edges may also be injured. Sharp edges are often chamfered or radiused to prevent unnecessary cuts to personnel and equipment.
The best way to prevent flash formation is to replace the workpiece with less ductile material. Using less ductile materials can cause unwanted parts to chip or separate from the main parts. Most of the time, however, this is not an option, especially for applications with stringent material requirements. The formation of burrs is almost unavoidable when machining ductile materials. Because of this, unconventional methods such as chemical etching and laser processing are ideal. However, these processes are limited in terms of limited workpiece thickness and high investment costs.
Different Types of Burrs
In addition to classifying burrs according to cutting direction, burrs can also be classified according to their formation mechanism. There are four types namely: Poisson, tumble, tear and cut off burrs.
1. Poisson Burr:
“Poisson” comes from the term Poisson effect, meaning expansion perpendicular to the direction of applied stress. Applying a compressive force to the material causes the edges of the contact area to plastically deform and elongate, creating burrs. During cutting, when the tip of the cutting tool hits the workpiece, the kerf edge deforms due to compressive and shearing forces. These deformations are seen as entry burrs that form at the entry point of the cutting tool.
2. Roll-over Burr :
These chips are curved rather than sheared from the toolpath. As the cutting tool exits the cut, some material rolls and moves with the tool. The material faces the feed and is folded along the cut edge. If the material is sufficiently ductile, the chips will not easily separate from the part. Depth of cut also contributes to the formation of rolling burrs because the chip or roll becomes thicker as the depth increases.
3. Tear Burr :
Tear burrs are edge burrs that occur when a cut part is plastically deformed rather than fully sheared. This is observed during punching, leaving sharp jagged edges along the contour of the punched hole. This is the material torn from the workpiece.
4. Cut-off Burr: :
Cutting burrs are the result of remaining material when the cut part separates from the main part or falls off. This can be a positive or negative glitch. Cutting burrs mainly appear on sawing and automatic screw machine parts. Prevent these types of burrs by properly supporting the sides until the cut is complete.
Types of deburring process
There are various methods of deburring, depending on the material, part geometry, size and location of the burr, product volume and cost. Manual and mechanical deburring operations are common methods of deburring. Electrochemistry, thermal energy and cryogenics are unconventional methods for specific deburring applications. Below are common deburring processes along with their respective benefits and applications.
1. Mass Finishing: :
This method is used when large numbers of parts/assemblies need to be finished, can be run as a batch system or as a continuous system, and can be performed as a dry or wet process (depending on the material of the product to be finished). Batch finishing requires input Time and materials to determine the exact batch finishing recipe that meets your needs, but saves time, money and manual labor in the long run. Some examples of batch finishing equipment include rotary vibrators, continuous flow units, drag finishers, high energy disc systems, and barrel vibrators.
2. Manual Deburring: :
This method refers to deburring operations using hand-held or mechanized tools using deburring tools, grinders, brushes, files, sanders, etc. The process is “localized” — meaning it doesn’t affect the entire part. Since the parameters for manual deburring cannot be perfectly defined, this method is used where there is a high tolerance for dimensional variations. Most manufacturers and manufacturers have internal time standards. However, these do not address issues regarding the consistency of the process. The process is slow and often done at the end of the line, where any mistakes can be costly to the manufacturer.
3. Robotic Deburring :
This involves chamfering, grinding or deburring tools mounted on robotic arms. Since the main disadvantages of manual deburring are inconsistency, slow turnaround, and labor-intensive, robotic deburring addresses these issues by eliminating the human element. Robots can perform repeatable actions continuously and rapidly. CNC programming allows the operator to input predefined motions and other parameters such as force and tool speed. Despite the higher initial cost, robotic deburring is beneficial in the long run as it reduces operating costs. Additionally, robotic systems are safer than manual systems.
4. Mechanical Deburring: :
Mechanical deburring uses a machine to perform general deburring of a workpiece. The operator has less control over the strength and positioning of the deburring action than manual deburring. Roller drums are one of the most economical deburring machines in terms of operating costs.
This equipment can not only remove burrs, but also polish the surface of parts. The machine works by loading one or more parts into a chamber or “bucket” along with grinding media. Depending on the material and surface finish, special compounds are also added. This is usually a batch operation, but online batch and single-pass processing are also available. In addition, barrel tumbling can be divided into wet tumbling and dry tumbling.
5. Vibratory Deburring :
Vibratory deburring machines are similar to deburring drums in that the parts are loaded into a chamber with abrasive media and other additional compounds. Their main difference is the movement of the chamber. This type of machine vibrates to create motion as the drum rotates to create agitation in the chamber. The chamber is mounted on a spring or damper, isolating its movement from the foundation. An eccentric rotating weight is attached to shake the contents of the chamber. Various configurations are available such as bucket, round bowl or trough machines. The choice of configuration depends on the geometry of the part and its application.
6. Electrochemical Deburring :
This is a deburring process using the principle of electrolysis. Electrolysis is accelerated in areas with small inter-electrode gaps. This is used to focus the electrolysis on the area where the burrs are. The workpiece attaches to the circuit and acts as the positive pole.
To complete the circuit, an electrolyte is added to transfer charge between the tool and workpiece. Part of the tool is insulated to prevent dissolving other surfaces. This method is suitable for deburring difficult-to-machine geometries and difficult-to-machine but conductive materials. A disadvantage of this process, however, is that wastewater treatment is difficult because it uses compounds that are harmful to the environment.
Conclusion
- Deburring is a secondary operation of the machining process that improves the final quality of the product by removing raised edges and unwanted chunks of material called Down.
- Burrs can create problems such as improper assembly and assembly of parts, shortened part life due to fatigue and corrosion, safety hazards, and loss of aesthetics.
- Burrs are classified according to the mechanism of formation. Classification as Poisson, flip, tear, cut off.
- There are various methods of deburring, depending on material, part geometry, size and location of burrs, product volume and cost. The most popular methods of deburring are manual and mechanical.
- Manual deburring includes brushing, sanding and rolling. Actions are performed by hand or powered machines.
- Mechanical deburring using rollers and vibrating machines. These machines perform general deburring of workpieces.
- For large-scale deburring operations (tumbling and vibration), use abrasive media. These can be ceramics, steel, plastics and organic compounds.
