Problem solving Analyzing tool life & insert failure

Transcription

1 Problem solving Analyzing tool life & insert failure 1/37

2 Practical optimization Structured approach to problem solving Yes No 2. Conditions facts & data type of tool cutting conditions workpiece matl, cooling, type of wear and tool life. 1. Problem identification focus cause vs. consequence. 3. Analysis cutting depth cutting matl. R a vs rε & feed cutting method. 4. Conclusions, recommendations and solutions. A problem is anything which deviates from expectations.??? 2/37

3 Some elements Practical optimization EFFECTS Increase cutting speed V C Increase feed f Increase cutting depth a p Productivity Heat Wear Power Cutting forces 3/37

4 Practical optimization Structured problem treatment rather than speculative approaches or solutions. Higher cutting speed (harder carbide grade) Long chips Vibrations Burring Crater wear Optimum cutting conditions Plastic deformation Chip hammering Insert breakage Insert build-up Notch wear Chipping Chip section (feed, cutting depth) (stronger chip breakage geometry) 4/37

5 Practical optimization Practical indications of excessive wear Insert wear... Higher power... Tolerances in workpiece... Surface finish... Burring... Heat development... Insert chipping... Poor heat dispersal... Poor chip control... Noise during machining... Vibrations... 5/37

6 Wear Land Development Practical optimization.040 Flank Wear Land A B C Time in Cut ( minutes ) A = Break in period and measurable wear B = Largest part of insert life and constant wear C = Increasing rate of wear (wear land becomes larger and larger) 6/37

7 Flank Wear Possible solutions Reduce the cutting speed. Select a more wear resistant grade. Abrasive wear. Hard micro inclusions in the workpiece cut into the insert. Small pieces of coating break off and also cut into the insert. The soft cobalt wears out of the matrix, the carbide grains no longer have any adhesion and therefore break off. 7/37

8 Practical optimization Cutting speed Depth of cut Feed rate Increasing by 50% Reduces tool life by DOC 0-10% Feed rate 60% Cutting speed 90% 8/37

9 Practical optimization Cutting edge wear 9/37

10 Cratering Possible solutions Diffusion, decomposition and abrasive wear. Hot chips decompose the cobalt and dissolve the WC. Hard micro inclusions in the workpiece cut into the insert. Small pieces of coating break off and also cut into the insert. The soft cobalt wears out of the matrix, the carbide grains no longer have any adhesion and therefore break off. Select a more wear resistant insert grade in the P area of application. Change the chipbreaker geometry. Use coolant. Reduce the cutting speed. 10/37

11 Built-Up Edge Possible solutions Increase the cutting speed. Use coolant Material adhesion. At a high pressure and low temperature, the workpiece material sticks to the cutting edge. This built-up edge breaks off and takespiecesof the coatingand substrate material with it. Select an insert with a sharper cutting edge geometry. Increase the feed. A distinction must be made between hard and soft chip welds. 11/37

12 Chipping Possible solutions Increase the cutting speed. Reduce the feed Chipping Reduce the risk of vibrations. the entrance or exit). Select a stronger cutting edge geometry Select a tougher grade Abrasive wear and local stress concentration. Hard micro inclusions in the workpiece material cause local stress concentration. Interrupted cuts and vibrations also cause local stress concentrations. 12/37

13 Thermal/Mechanical Failure Possible solutions Rapid change in the thermal load. Temperature differences between warm and cold zones cause thermal stress. Fatigue leads to cracking. Use an abundant supply of coolant. Do not use coolant. Reduce the cutting speed. Reduce the feed. Select a tougher hard insert grade. Use a different machining method (ratio between time in cut and time out of cut). 13/37

14 Edge Deformation Possible solutions Mechanical and thermal overloading. The heat softens the insert structure. The cobalt softens and the insert becomes deformed. Reduce the cutting speed. Reduce the feed. Select a more wear resistant insert grade. Use coolant. Select an insert with a larger nose radius. 14/37

15 Notching Possible solutions Oxidation (machining surface) and local stress concentration (clearance surface). The complex W a Fe b Co c O d formed at high temperatures breaks off. Surface hardening (previous cut) and hard micro inclusions in the workpiece material cause a notch where the workpiece comes into contact with the cutting edge. Select a more wear resistant insert grade (oxidation). Reduce the cutting speed (oxidation). Reduce the feed (oxidation). Select a tougher insert grade. Select a smaller entering angle. 15/37

16 Chip Hammering Possible solutions Change the feed. Change the cutting depth. Select a entrance angle k. Abrasive wear and mechanical overload. The chips collide with the cutting edge and damage it. Select a different chip-breaker geometry. Select a tougher insert grade. 16/37

17 Mechanical Fracture Possible solutions Mechanical overload. The combination of mechanical and thermal load is so great that the insert breaks during the first cuts (seconds). One of the previous wear points has become too large. Reduce the feed. Reduce the cutting depth. Select a tougher insert grade. Select an insert with a stronger cutting edge or with a chip-breaker geometry for larger feeds. Select a thicker insert. Check the workpiece for hard inclusions or difficult entry. 17/37

18 DURATOMIC TM 18/37

19 What is Duratomic TM? 19/37

20 Which impresses you the most? Both are made from carbon,... but what a difference a change in atomic structure makes! 20/37

21 Which impresses you the most? Both are made from aluminum oxide,... but what a difference a change in atomic structure makes! 21/37

22 DURATOMIC 22/37

23 DURATOMIC Column/grain boundary 23/37