Secondary Machining

All machine manufacturing / metal fabrication facilities have seen great improvements - precision aerospace parts in particular are where increased quality and reduced risk is the mantra, and new technologies in manufacturing are constantly being developed and implemented towards the end of achieving zero defects. One of the very simple yet most dangerous issues is burrs on a finished product - should a part with a hanging burr get assembled, catastrophic accidents may occur so, all machining processes must be designed where the deburring process is processed either inside the machining operation or by manual deburring.

What is a burr?

A burr or a raised edge or a small piece of ‘raised’ material on a workpiece left behind by a cutting tool - in short, they are sharp edges can cause injuries in part handling when not removed and damage to the final assembly if installed. The process removing burr is called as deburring. Deburring accounts for a significant portion of manufacturing costs.

Why Is Deburring Needed?

Any displaced material from machining can cause critical and hazardous issues. For example, if a small piece of material peeling off from a part used in the food industry was consumed - it’d obviously be a huge health hazard. Likewise in the aerospace and automotive industries high precision parts having any burrs or loose edges can impeded functionality and/or cause major issues in assembly resulting in accidents. Medical products such as like surgical tools and implants must have smooth rounded edges which otherwise could cause internal damage when use inside a surgical process or when implanted inside the body.

Also, without deburring, it is very difficult for part handling and burrs can cause many work injuries either in moving parts, during machining operations, inspection, etc. Nobody wants to handle sharp things.

Deburring is therefore a very important step which needs to be considered when establishing all machining operation. and only deburred parts with smooth surfaces can be successfully processed through any subsequent operations.

Different types of burrs?

Burrs are not one size and one type - they can vary depending on machining process and amount of material removal, wear on machine tools, etc.. Various high speed machining techniques can cause burrs. Abrasive machining (Grinding, Honing, Waterjet) are typically burr free processes.... but some can cause burrs, and some of the most common burrs are :

• Rollover burrs - This is the most common type of burr, which is generally formed as a tool exits the workpiece. The size of burr depends on the amount of material removed in the process or the wear on the tool or a combination of both. High material removal in each pass can create a huge burrs. A dull cutting tool can cause a huge burr. The best choice is to preform multiple passes of less material removal along with an optimized tool change / resharpening frequency.
• Tear Burrs - These are formed during material deformation. Common machining processes that can cause tear burrs are from broaching, coining, stamping.
• Breakoff Burrs / Cut-off Burrs - These are formed when work piece get’s separated from material during cut-off.
• Poisson Burrs - These are formed when the tool is applied to a workpiece under a downward force. The machined material bulges outwards and can occur on the edge of the workpiece when the tool is removed from the surface.

Different types of Deburring Methods?

There are many ways of deburring methods available. In addition to optimizing the machining process in reducing the size of the burrs, the most appropriate and cost-effective method is researched and implemented.

• Machine Deburring - This is one of the most easiest and cost-effective process of deburring. A deburring tool recut’s the metal surface which has burrs and deburrs the part. The deburring tool generally break’s sharp edges by chamfering them and in the process remove burrs on metal parts. Some deburring tools cannot reach some metal surfaces on some small parts and/or those with complex geometries and need to be deburred using other techniques.

• Manual Deburring - This requires a very skilled and intensive process. Appropriate instructions needs to be conveyed to the operator before deburring otherwise the operator might get injured or can damage scrap the workpiece by under or over buffing the part damaging the surface finish in the deburring process. There are many hand deburring tools operators use - some of the manual deburring tools are buffing wheels, high speed hand held dremel, counter sink blades, file, deburring blades, bench grinders, various abrasive wheels, belt sanders and many more.

  Manual deburring can get complicated when deburring small parts. This is because of heat dissipated while deburring along with the difficulty of gripping of small parts.

• Automated Deburring - Manual deburring can get complicated with smaller parts so often times automation can enhance the process of deburring and creating a robotic cost-effective deburring process.
• Thermal Energy Deburring - This is a process where heat is used to vaporize the burr. The process is very quick and uses hot and corrosive gases, applied in short bursts to cause the burr to heat up and eventually dissolve. Materials that have low conductivity are good choice to use this deburring process.
• Electrochemical Deburring - This process uses electrolysis to remove the burrs. The part is attached to a circuit and submerged in the electrolyte. The insulated tool acts as a cathode while the part is anode and electricity will dissolve the burr. This is a part specific process and hence it can be highly accurate.

In short, parts should always be burr free after all the machining process, and appropriate cost-effective efficient technique must be chosen to remove all of these burrs so that the workpieces retain dimensional accuracy and functionality.