Laser hardening has gained significant traction in the United States, becoming a favored method among OEMs and smaller tool and die makers. Each die is unique, requiring the laser to follow precise paths at specific angles and orientations to ensure quality. Robots are commonly used for this process due to their flexibility. This article explores two primary methods of robotic programming used in laser hardening operations and highlights the advantages of one approach over the other.

Methods of Programming Robots for Laser Hardening

Robotic tool path motion for dies is typically programmed in one of two ways:

  1. Tool Path Software Programming
  2. Manual Touch-up – Moving the robotic head to each point and saving the position manually.

Advantages of Tool Path Software Programming Over Manual Touch-up

  1. Reduced Lead Time

With tool path software, the robotic path can be simulated and tested before the dies even arrive. This preemptive approach significantly reduces lead time for customers. In contrast, manual touch-up requires the die to be physically present, often adding substantial delays. Additionally, Synergy’s capability to run dies in a lights-out operation further accelerates delivery times.

Picture 1: Tool path motion simulated and tested in software prior to receiving the die thereby reducing the lead time. 

  1. Optimized Laser Start, Stop, and Overlap Locations

When laser heat treating circular profiles and circumferential profiles such as draw beads,  the laser often returns to its starting point, resulting in overlap. This overlap can cause a loss of hardness due to annealing at start/stop area. Synergy has conducted extensive process development to optimize these overlap regions, minimizing hardness loss to just a few points. Precise tool path motion is crucial for this optimization, which is difficult to achieve with manual programming. Manual methods can lead to excessive hardness loss, larger soft spots on the die, and inconsistent results which could show up later in the service life of the die.  

Picture 2: Simulation of circumferential paths with minimal overlap regions 

  1. Enhanced Quality and Consistency of Hardness Profiles

Stamping dies often require hardening on male radii, which can range from 3 mm to 25 mm or more. To properly harden these critical areas where metal rubs against the die with the most force, it’s essential to orient the laser beam accurately. Tool path programming ensures a consistent and precise angle of incidence, whereas manual touch-ups rely on the operator’s judgment, potentially leading to poor locational accuracy. Tool path programming also guarantees consistent laser beam travel speeds around complex tool motions, resulting in superior consistency in hardness values (+/- 1 HRC). Manually achieving this consistency, especially in complex profiles, is both challenging and time-consuming.

  1. Consistent Overlap in Surface Areas

Laser hardening of binder and cavity surfaces is often required in stamping dies for materials like aluminum. When hardening large surface areas, overlapping previously hardened laser paths is necessary. However, overlap regions can experience hardness loss to the next laser pass annealing the previous pass. If there is a steep contrast in hard and soft regions, wavey pattern shows up on the stamped part and requires substantial post work from die maker. Synergy’s extensive research has led to process recipes that minimize distortion and hardness loss in these areas. These process recipes involve laying the hardening tracks of right size and heat in very precise locations to minimize the soft spots and avoid wavy pattern. This level of consistency is only possible through tool path programming.

Picture 3: Laser hardening of large surfaces with precision overlap

  1. Cost Considerations

Manual touchup programming is cost-effective for smaller, simpler tools. However, as die complexity increases, tool path programming and lights-out operations offer substantial value to customers.

Summary

While some benefits discussed in this article may not be immediately visible to the naked eye, OEM customers have observed that robotic laser hardening operations programmed with tool path software can prevent long-term die performance issues. The durability and performance advantages of dies programmed with tool path software far outweigh the slight cost savings that may be associated with manual programming.