Anodizing is an electrochemical process that creates a decorative and durable coating on aluminum. The process contains multiple variables that are complex and do require an understanding and commitment to best practices and risk management. The difficult challenge for any anodizer is first making sure that the goals and expectations of the manufacturer are understood. Metal finishing is that final step in the supply chain before delivery of a finished good which requires the utmost in attention to detail.
There are things that anodizing can do, and there are things that anodizing cannot do. When we hear customers say “don’t you just dip it?” related to the anodizing process it brings up all sorts of red flags for us. It is easy to “blame the anodizer” when things go wrong in the process. In the 40 years that Alpha Metal Finishing has served the manufacturing industry we have found many critical factors involved from beginning to end in providing consistent, high quality results in anodizing. Here are just five of the top factors that we feel impact quality:
1. Source Material
The aluminum alloy itself can determine the final result of the anodizing finish in many ways. Each alloy has a different composition of alloying elements, some of which anodize very well and others not so much. For example, 6061 aluminum is one of the most popular alloys chosen by machine shops and manufacturers for its strength, surface finish, corrosion resistance to atmospheric conditions and its workability.
After choosing the appropriate alloy, it is important to use the same lot if possible throughout the job. There can be variations in the stock from the supplier. The quality of the stock (primary vs. secondary) from the supplier as well as how it was forged or extruded can have a significant impact on the final result of the finish after anodizing. For more information on alloys suitable for anodizing we recommend visiting the Aluminum Anodizers Council website at http://www.anodizing.org/?page=alloys.
2. Surface Preparation
Anodizing is unlike any other finishing process in that it reveals the substrate of the aluminum during processing, much like film development. For this reason it is very important to consider every aspect of the surface preparation of the aluminum prior to being sent for anodizing. Proper handling and care of the aluminum parts on the machine shop floor will ensure consistent results in the anodizing process. Alpha has created an excellent resource for how to prepare the aluminum parts at: http://www.alphametal.com/resources/important-tips-prior-to-anodizing.
3. Chemistry Is Critical
One of the most critical components to creating quality, consistent results in anodizing is maintaining tight controls on the chemistry of each bath. There are multiple steps to the process of anodizing which include: cleaning, pre-treatment (etch), anodizing, coloring (except for clear), sealing, and of course there are multiple rinses in between each of these steps.
The controls that must be maintained in each of the steps are: PH, concentration, temperature, as well as time. Chemical suppliers do recommend a range of parameters for each chemical but it is important for each anodizer to do their own research and testing to find an optimal range. This can be done with the assistance of chemical management software as well as consulting with the chemical supplier.
4. Anodizing Tank Controls
The actual step of anodizing requires maintaining multiple controls of the tank itself in order to ensure a consistent, quality coating. Aside from the chemistry of the tank (already mentioned) it is critical to calibrate the electrical source (rectifier) on a regular schedule.
Anodizing time, temperature, agitation and quality of cathodes in the tank also come into play and can impact the final result of the coating on parts during the anodizing process.
5. People Who Care
It would seem obvious that a measure of success in anodizing requires people who are not only competent and knowledgeable but also care about what they are doing. However, in our experience it is painfully surprising to find that many companies do not recognize that their culture is creating the less than desirable results that they are encountering. Principle #5 of The Toyota Way states: “Build a culture of stopping to fix problems, to get quality right the first time.” Principle #12 also applies: “Go and see for yourself to thoroughly understand the situation.” –The Toyota Way, Jeffrey Liker
At Alpha Metal Finishing, we strive to build a culture of people who care and want to create a remarkable experience. We do our best to build relational partnerships as opposed to just transactional ones. Some of the key things to review with a potential anodizer (and really any supplier) are:
Again, there are many details and variables involved in producing high quality anodizing but these are some of primary ones that will help avoid unnecessary reworks or frustration on both sides. When things go right in the anodizing process everyone wins. When things go wrong, finger pointing is easy and rather common. Having a focus on problem solving and a willingness to learn is the key to producing high quality results that make both suppliers and customers happy. For more information on understanding and specifying anodizing we recommend the following resource from Joseph Osborn at OMW Corporation: http://www.omwcorp.com/wp-content/uploads/2018/02/Understanding-and-Specifying-Anodizing.pdf.
Anodizing grows perpendicular to the surface of the aluminum. That being said, whatever surface roughness/texture is there before anodizing will be there after anodizing process. Anodizing is only .0003 to .002 inches thick and has little effect on the mechanical properties. Optically, there will be a change in the emissivity of the anodized surface.
Alpha often comes across strange and bizarre challenges with some of our customer parts when it comes to the anodizing process. With one medical device manufacturer this was definitely the case. We had been presented with a new part that when we finished the anodizing process it revealed microscopic pits in the surface.
We scratched our heads, came up with a rework process and then tried running it again. The same problem occurred. Now, this particular part was a 2024 alloy which already created a few challenges related to etching. After a conference call and face to face meeting with the customer we tried again on some new, raw parts. The pits came through the substrate again! The substrate was inspected each time and it was initially thought that perhaps there were extrusion lines or possibly bad material in the original stock of the alloy that could not be visibly seen.
During the anodizing process if there are “junk” elements in the alloy they can fall out in the process, potentially causing pits. This is one of the reasons we ask our customers at times where they actually purchased their aluminum stock. If the stock or extrusion has any issues the anodizing process will only reveal the imperfections in the substrate. It would be nice if anodizing could cover up machine marks, extrusion lines, or variations in the substrate, but unfortunately it cannot.
Without any solid answers to the problem at that point, we were all frustrated and feeling a little sheepish that we could not find a solution for our customer. Then, it occurred to one of our team members: how were the parts being machined? We asked the customer and discovered that after machining the parts they were belt sanded. Aha! With a few more questions we further discovered that the belt sander was also used on steel parts as well. Any steel particles embedded in the aluminum substrate will not react well with the anodizing process! Kind of like what Captain Ramius told Jack Ryan in The Hunt for Red October: “Hey, Ryan, be careful what you shoot at. Most things in here don't react too well to bullets."
With this new knowledge we were able to inform the customer that they needed to change the belt prior to sanding the aluminum parts. Once they did that, we had no more issues with pits showing up in their parts. Nobody particularly likes pits, and we certainly don’t like them in anodizing.
For more on this issue we recommend Anodic Coating Defects, Their Causes & Cure by Arthur W. Brace. Also, see Robert Probert’s response to this question at http://www.finishing.com/481/64.shtml
It’s fairly obvious in this difficult economy that companies have no choice but to change in order to survive, let alone thrive. The world is moving and shifting so fast that companies who fail to adapt their thinking, processes, and systems are being left behind and closing their doors. Alpha could have been one of those sad stories. Fortunately, the story hasn’t ended and we’re happy to say that we’ve turned a corner.
I faced many new challenges when I started at Alpha in 2010, the main one being that I said I would never work in my father’s anodizing business. God must have a great sense of humor when we use the word “never.” We were in a downward spiral and the morale of the staff was at an all-time low. We needed more than just a new strategy in sales and quality, but a serious overhaul in the attitude and focus of the leadership. As I read “How the Mighty Fall” by Jim Collins I couldn’t help but think that we were experiencing the silent creep of doom. Call me a bit naïve since I’m new to the anodizing industry, but I came in with a sense of urgency and started with what I knew we needed to do before we could have any discussions: grow sales. I’m sure the management team must have thought I was crazy. We hired in a great sales person to assist me in mining the opportunities for business development that lay dormant, many that were just plain missed.
Ben Franklin once said “Drive thy business or it will drive thee.” For me, that means you can’t just sit there and expect business to come to you through your normal supply chains, especially if the economy is hurting. You have to go get the business, proactively! As it was, my salesperson and I put together a great strategy for marketing and sales. What we didn’t anticipate is that we would meet resistance at every step of the journey from the management team. Oh, they nodded their heads at our ideas and tried to smile but it was obvious that they thought “He just doesn’t get it.” For us, the change meant excitement.
"Change has a considerable psychological impact on the human mind. To the fearful it is threatening because it means that things may get worse. To the hopeful it is encouraging because things may get better. To the confident it is inspiring because the challenge exists to make things better." --King Whitney Jr.
I must confess, I really thought that they would eventually catch the vision and excitement for what I saw as great potential for Alpha. Unfortunately, they had no desire to take things any farther. All change is painful and can produce a certain amount of fear, even complacency. The pain and consequences of not making changes though can be even worse. As the sales started to grow within a few months I detected a slight spark of enthusiasm, but when the growing pains came with it I knew the managers were not along for the ride. It was time to make the hard decisions from the top down: the managers needed to go. For sure, there was much agonizing over this decision. If Alpha was ever going to get back off the ground we needed a transformation in the leadership and culture. At a previous company I worked for I experienced firsthand the devastating effects of having the wrong leaders at the top. It damaged momentum, morale, and caused sales and service delivery to decline. We couldn’t allow this to happen at Alpha.
Winston Churchill followed three basic principles in selecting his personnel: 1. Pick the best person suited for the job and ignore seniority. 2. Have your plans in mind as you select your executives so that they serve your design and not their own. 3. Start at the top, not the bottom, in building your team. That is essentially the strategy that we followed as we replaced three good managers. I had taken quite a bit of time to identify leaders within the current staff at Alpha so that when the time came to lay off two of our managers we had a transition plan in place. One manager seemed to be on board with us and showed a willingness to hang in there. Ultimately, the change was just too stressful for him so he opted to resign.
I wish I could say that this transition was smooth. It was not! No leadership change is ever perfectly smooth and certainly we experienced a great loss in our knowledge base as well as the investment in their training. Not to mention, there were major hiccups in quality and production for about three months as the new leadership team learned their new roles. Were there some mistakes made in how we handled the leadership transition? Definitely. It was difficult to think through how all of the changes would impact us and the rest of the staff. We did not have the luxury of a change management team. But we kept moving forward with the principles from Jim Collins' Good to Great: “Those who build great organizations make sure they have the right people on the bus, the wrong people off the bus.”
Some of you may be asking “Was there a payoff?” Most assuredly. In the past two years we have experienced solid growth in sales (nearly 20%) as well as a huge change in the morale and productivity of the staff. Not to mention we have received many compliments from our long time customers. We haven’t hit all of our goals and objectives but as the new leadership team has begun to gel and find their groove in how they work together it is clear that we made the right decision. Was the transition easy? No. Was it painful? Yes. But I’d rather have growing pains any day. Surviving these hard economic times is good but we make it our aim to thrive, not just survive. That takes unwavering faith in what you’re doing and why.
During the anodizing process, the aluminum oxide film grows perpendicular to the surface of the part. Because of this there will be less coverage on the sharp corners of parts leaving a thin spot in the anodic coating. That thin spot will then be a site of low dielectric strength and reduced corrosion resistance. In the case of parts being hard anodized, because it is a site of low electrical resistance, an increased amount of current will flow at that spot, frequently causing the part to overheat and produce a discoloration or “burn”. In some cases the temperature becomes so hot that the anodic coating and the underlying aluminum are actually dissolved in the sulfuric acid electrolyte and large amounts of material are removed from the part.
This phenomenon very rarely causes a problem in conventional anodizing. However, in the hardcoat anodizing process where power densities can approach 3000 watts per square foot, sharp corners or points can initiate a “burn” which can destroy portions of the part. Being aware of this potential problem, Alpha Metal Finishing has developed procedures and computer control technology that will minimize this possibility. However it is much better practice to design parts without sharp points or edges.
A different but equally undesirable phenomenon occurs with sharp inside corners. The two surfaces growing perpendicular to each other impinge upon each other at the corner creating a seam. The seam is not contiguous like normal anodizing and can expand and contract with temperature allowing the environment access to the base aluminum at its root. MIL-A-8625 recommends a minimum radius of .030 in. on both inside and outside corners.
Anodizing is the process of electrochemically converting the surface of an aluminum part to aluminum oxide. Aluminum oxide occupies about two times the volume as that of raw aluminum. Therefore, anodizing will cause parts to grow dimensionally. This factor should be taken into consideration when designing parts that will be anodized.
Typical standard clear and color anodizing creates an aluminum oxide film in the range of .0002 to .0008 inches, (.005 to .020 mm), on each surface. Hard anodizing is typically in the range of .0005 to .003 inches, (.013 to .076 mm), the most common being .002 inches. (.051 mm).
The process of hard anodizing a part to .002 in. film thickness will therefore grow .001 in. on each surface or .002 in. in overall dimension.
Higher purity alloys are always preferred for anodizing. Alloying elements such as copper and silicon do not anodize and leave microscopic voids in the aluminum oxide film. Since the anodizing process converts only the aluminum to aluminum oxide to form the anodized finish, higher purity aluminum will yield a denser and harder layer of aluminum oxide. High concentrations of some alloying elements will also affect the surface finish and color of the anodized finish and will reduce the effectiveness of the sealing process causing reduced corrosion and wear resistance and decreasing fade resistance in dyed parts.
The most popular alloys used for anodizing are 5000, 6000 and 7000 series alloys. These alloys will provide consistently excellent quality finishes for hardcoat and conventional anodizing. High purity alloys like 1100 and 3000 series will also form very good finishes. Although 2000 series alloys are popular alloys because of their strength and machining characteristics ithey are not the best choice for good anodized finishes because of their high copper content. It has all of the disadvantages noted in the above paragraph. Alpha Metal Finishing regularly provides good anodized finishes for parts made from 2000 series alloys, however a superior anodized finish will be obtained with higher purity alloys.
Anodizing is an electrolytic process for producing controlled aluminum oxide films on aluminum. Oxide forms naturally on untreated aluminum, but the anodizing process produces a coating which is uniform, much harder, and more dense than natural oxidation. Aluminium oxide also possesses excellent thermal and electrical insulating qualities.
The anodic film is formed by converting the surface of the part into aluminum oxide. Unlike paint, which can flake off if not applied properly, anodized aluminum finishes are actually formed from the original material and cannot flake off. The aluminum oxide finish is very hard and exceptionally wear resistant. Anodizing is good for many consumer products and sporting goods due to its aesthetic and corrosion protection properties. Anodizing is the primary finish for aluminum aircraft parts including major components before assembly and painting. We also offer Teflon impregnation to further enhance your parts resistance to wear.
Parts can be dyed during the anodizing process to produce luxurious finishes with a deep color that can only be imitated by paint. Alpha Metal Finishing currently offers aluminum anodizing in clear, black, gold, red, blue, and green. A variety of other colors are available for your higher volume products.
At Alpha Metal, our standard anodizing process conforms to MIL-A-8625 Type II.
Benefits of Aluminum Anodizing: