In the last blog of our series that focuses on key steps and challenges in laser process development, I explained three common mistakes in selecting laser. Now I want to talk about how we approach this early phase, which we call Phase One in our methodology when we work out what's the right type of laser.
There are the 10 steps I typically follow on an application to application basis.
Step 1: Articulate the application
One way I like to do this is to listen to our customers’ big picture, product vision, and the process needs. And then I like to re-articulate what I learned in the form of a document that describes this problem-and-needs statement.
And if our customers think that we've grasped this problem correctly, we move on from there. If not, then we discuss it more, identify the misalignment and redo the document until there is good alignment in our understanding of what their needs are.
Step 2: Review the materials
Carefully review the materials that need to be processed. Now, sometimes it's just a single material. It could be a wafer of glass or semiconductor. Sometimes it's a complex medical device where there may be five or six different materials that laser might come in contact with, or a display panel where you have multiple stacks of materials and you might want to process just the top material and the bottom materials or vice versa.
To understand the materials better, find out:
how many materials the laser is going to process?
what is the proximity of the laser to other materials and the devices
what are the wavelengths that these materials are going to absorb or transmit
what are the thermal properties of these materials
what are the mechanical and chemical properties of these materials
Step 3: Know the deal breakers
By identifying what type of byproducts or features defects are deal breakers, applications engineers can now have boundaries to this very large process space.
For example, if you find out any type of slag, burr, micro crack or anything like that is an absolute deal breaker, then it kind of pushes us towards a regime where we need to work with short pulse lasers as a potential solution, or maybe working with ultraviolet laser, or maybe we can get away with another laser as well, but we would need to make sure it does not yield any of the deal-breaking defects.
Having these boundaries can help save money. Typically, an absolutely perfect result requires a very expensive and slow solution. A lot of the times, we will have to go down that route when asked, then find out that really at the end of the day, the end application can tolerate having some microscopic defects in there if another process can be two, three, four, sometimes even 10 times cheaper as a return on investment. So clear articulation of the deal breakers is important.
Step 4: Understanding throughput needs
Work out the throughput requirements and find out why the throughput requirements are set up that way. I like to challenge these numbers all the time and work out what's driving throughput requirements because misleading statements in this place can mistakenly eliminate potential solutions that might be a great fit for your application.
And there're many ways to scale throughput with lasers systems -- from multiple heads, multiple lasers, splitting the beam into multiple focal spots or just running at a higher power with faster beam delivery systems.
Being mindful that this phase isn't trying to work out how to make everything fast and perfect is important so to not be discouraged or distracted.
It’s worthy to note at this early Phase One, the process can be super slow. Being mindful that this phase isn't trying to work out how to make everything fast and perfect is important so to not be discouraged or distracted. Remember this phase is about working out what the right type of laser is and then using that as a platform to get to where you need to be.
The important focus at this stage is to evaluate quality and identify pathways to speeding things up. Having said that, there are some applications where speed is everything, and if you know that it is not financially feasible at a certain speed, for example one part per minute, then it's good to communicate that early on and have that as one of the deal breakers (Step 3).
Step 5: What are the part or material tolerances?
Now, I'm not talking about tolerances to the processes as those are identified early on in Step 1.What I mean here is the material that you would put into the machine or the product that you've developed that you put into machine--what are the tolerances on this? Something to note is that in general, most industrial lasers have extremely low variability, which means that the power, the size of the laser beam and all the key parameters that determine the process are very, very robust.
Where we see most of the variations that happen in processing are caused by the materials or parts themselves--for example, the flatness of the materials or how well aligned the materials are to certain features.
A lot of processes can show variation(s). For instance, in laser drilling, you may drill a bunch of holes in your material, and find the exact size of the hole varies quite a lot. You’d find often that this is caused by the material which can be its density, flatness, thickness, surface smoothness, or even how debris is being handled etc.
If we look at laser welding, variations can happen based on how well the material is assembled ahead of time, how well the two parts to be welded together are placed in contact with each other, or the cleanliness of the material and the presence of defects.
So understand what the tolerances are going to be on the material and it's important to know what these tolerances would be like in a production environment. Sometimes the parts that we get in at an early stage have been handled many times before they come into our facility, and they've not been done in a nice production environment. And so we're working with parts that are a lot dirtier than you would have in production. So this could present challenges. Sometimes it's the opposite. Sometimes production environment is actually really dirty and the parts that we're getting in have all been handled in a clean room. And now the parts are too clean in that regard. So it's good to have an understanding what the production environment is going to be like.
Step 6: Research laser prior arts
Step 1 to Step 5 are guidelines on how to hold theoretical discussions with our customers so that we can have a deeper understanding of the requirements. Once that is established, it is now a good time to look at what's been done in the past. At this point, we look to our knowledge base through the following:
we look into applications we've run before
we consult with our applications engineers and lean on their expertise.
we talk to our laser suppliers and learn from what they've learnt from in the past.
we research through published literature. One virtue of the laser industry is the strong community of both industrial and academic publications out. There’s much we can lean on to learn from the fundamental basics that are published.
Also it's really important to avoid draw conclusions too quickly. This step is as an exercise to mine possibilities and ideas as a start. For instance, you may find applications that had drilled 50 micron holes in borosilicate glass, but it’s important to know that you are not necessarily limited to the same features or results. Another example: you may find applications that drill one hole per minute, but there may be other beam delivery or laser systems that can speed things up.
To sum up this step, stay open minded as you learn and focus on understanding the fundamental laser material interaction and compatibility.
Step 7: Identify laser candidates
Form a general idea on what types of lasers could be potential candidates. Start reviewing the process requirements (Step 1 to 5), thinking about beam delivery, or talking to your applications engineer about beam delivery.
The choice of the beam delivery and how you use the laser can be the difference between getting an amazing result and having a complete failure. And often the difference between those two can be a choice of lens, the gas pressure that's used in a gas head, or maybe other subtle process nuance related to part fixtures.
Step 8: Design of experiments (DOEs)
We've finally got to a point now where we're running experiments in the lab, testing out different laser types and laser setups. One of the most important things to apply here is running experiments that vary the key parameters and look for trends. Now, this is basic scientific methodology, adjusting one variable at a time, and looking at trends when that variables is adjusted. Most laser labs have PhD-level applications engineers and scientists running these applications. But it’s also very common that good scientific methodology isn't used, either due to lack of staff or time constraints.
Most laser labs have PhD-level applications engineers and scientists running these applications. But it’s also very common that good scientific methodology isn't used, either due to lack of staff or time constraints.
Even though this stage is basically a simple test, it's pertinent that DOEs are set up and processes are adjusted in a way such that when you're comparing these process regimes, you understand the trends and how they came to be. Whether you're just trying to look at the dependency of laser power, wavelength, beam delivery, or even comparing two completely different types of lasers, you need to analyze the results in a way such that: 1. it makes sense
2. you're able to learn about these trends
3. you understand how specific parameters are affecting the process.
The emphasis in this step is to look for trends using good scientific methodology.
Step 9: Configure optical beam delivery
Make sure that the beam delivery and optics are set up to be in the right regime. It's really important that you have the correct focus conditions to get the result that's required and defined by the process needs.
It’s good in this step to do some calculations. Maybe look into some of the background work that has been done that will help identify the sort of optics conditions you need to work in.
I have learned that some applications are a lot more sensitive to this than others. Good examples are glass cutting, glass welding, or applications where focusing conditions are absolutely critical, and they can make a difference between a working process and a complete failure. There are some applications such as hole drilling, where the size of the focus is going to be super critical as well.
Besides working on achieving the process, it’s also helpful to be mindful of practicalities like material handling and flatness from part to part. While you might not be trying to solve these problems in Phase One, you might be running into some issues if you come up with a solution in Phase One that absolutely relies on a specific optical setup which proves to be impractical in volume production and integration with automation. So just having some sort of awareness about those limitations is important here.
Step 10: Review. Refine. Report.
Now it’s time to take all these results and review them together with both the laser supplier and the customer to identify areas where the process can be improved, where it looks to be satisfactory, and to determine if you found a regime that has the potential to pass all of the deal breakers and meet the specifications.
It's at this last step where I compiled all the lessons learned into a report which we discuss together and create appropriate action plan for Phase Two – a phase where we attempt to make the parts to specifications.
To conclude, determining the right laser, which we call Phase One, is a great opportunity to create a space of solving your application requirements. By avoiding the three common mistakes I mentioned in the previous blog, and by approaching Phase One from a methodical scientific approach (the steps in this article) with experts in this space can lead to significantly better results, faster and more cost effective way of achieving overall success.
I hope this blog post is being useful for those who are interested in laser manufacturing, laser process developments, or just want to learn about how to get into the space. If you have any questions regarding phase one, or how to approach it, please reach out to us. Next blog post will be on phase two, which is making the part to spec, so stay tuned.
About Mark Turner