Glossary: What is ‘burr’ in die machining? – A comprehensive guide covering causes and countermeasures
- SANKO GOSEI
- 20 hours ago
- 3 min read
In the field of mold machining, the term ‘burr’ is frequently encountered. Although minute in size, this phenomenon has a significant impact on product quality, functionality and safety, and must not be taken lightly. In this article, we will explain in detail what a ‘burr’ is in the context of mold machining, its causes, the issues it presents, and methods for preventing and removing it.
◆ What is a burr?
A ‘burr’ refers to the minute protrusions or raised edges that form on the machined edges of a material during processes such as cutting or drilling. Whilst the term ‘burr’ is used in English, the Japanese term ‘kaeri’ is also commonly used in Japanese manufacturing environments.
In die and mold machining, burrs can form on edges and corners, particularly during processes such as electrical discharge machining (EDM), wire cutting, milling and grinding. The risk of burr formation is especially high when machining intricate shapes, thin-walled sections or hard materials.
◆ Causes of Burrs
The causes of burrs in mold machining depend heavily on the machining method and the characteristics of the material. The main causes are as follows:
Tool wear during cutting: When a tool becomes dull, it cannot cut the material cleanly, causing the material to be ‘pushed out’ and resulting in burrs.
Inappropriate feed rates or cutting conditions: If the feed rate is too high or the depth of cut is too great, excessive stress is placed on the material, promoting the formation of burrs.
Insufficient finishing passes in wire cutting: If the process is concluded after roughing only, burrs characteristic of wire cutting are likely to remain on the edges.
Thermal effects: In electrical discharge machining (EDM), localised high temperatures cause the material surface to melt and solidify again. During this process, minute protrusions (burrs) may form on the surface.
◆ Problems caused by burrs
Although burrs may appear to be nothing more than small protrusions at first glance, they have the potential to seriously affect the quality and durability of molds, as well as the molded products themselves.
Ploblem | Contents |
Transfer printing onto molded products | During molding, flash may be transferred directly to the resin, resulting in unwanted burrs |
Inadequate sealing of the parting line | If there is a draft, a gap will form during mold clamping, causing flash (molding burrs). |
Defective mold assembly | If there is a burr on the mating surface of a component, it cannot be assembled correctly |
Coating and Plating Defects | The coating does not adhere properly to the return section, leading to delamination or abnormal film formation |
Damage to tools or injuries to workers | Kicking back can shorten the life of the tool and also pose a risk of the operator cutting their fingers |
◆ Methods for Removing Flash (Deburring)
In mold manufacturing, the removal of flash is an essential part of the finishing process. The main methods are as follows.
1. Manual methods (files and sandpaper)
A method in which skilled workers remove flash whilst visually inspecting the workpiece. This is effective for small batches and precision parts, but is time-consuming.
2. Precision grinding (stone lapping)
The surface is levelled using grinding wheels or lapping discs. This process is applied to parting surfaces and core pins, amongst other areas.
3. Electrochemical deburring (ECM)
This process uses an electrolyte to uniformly remove burrs from fine, complex areas; however, it requires significant investment in both cost and equipment.
4. Finishing by Wire Cutting
Increasing the number of finishing passes during wire cutting can minimise the occurrence of burrs.
◆ Design Considerations to Minimise Burr Formation
● Tool Selection and Maintenance
When machining high-hardness die steel, the use of highly wear-resistant coated tools or carbide tools, combined with regular regrinding, can help suppress burr formation.
● Optimisation of Machining Sequence
Care must be taken to ensure that burrs do not remain on the final surface by considering the order of roughing and finishing operations, as well as the machining direction.
● Addition of Chamfers and Radii
Particularly in mating surfaces and parting line areas, incorporating chamfers or radii at the design stage helps to prevent the formation of burrs.
◆ Summary
Although ‘burrs’ in mold machining are often overlooked, they are a critical factor that significantly impacts product quality and mold performance. By reviewing machining conditions, selecting appropriate tools, ensuring thorough removal, and taking precautions at the design stage, the occurrence of burrs can be minimised.
It is precisely in molds where precision is paramount that the management of flash contributes to the overall reliability of the product. On the production floor, countermeasures against flash will remain an indispensable focus as a symbol of ‘invisible quality’.
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