Karl Hollis, technical sales manager, Precision Micro
Chemical etching has proved an exceptional sheet metal machining technology for complex, safety critical and exacting precision metal parts and components produced across all key industry sectors. Furthermore, it is opening up design possibilities that have until now been considered unachievable.
There are manufacturing engineers at countless OEMs who question which metal fabricating process would be the best fit for their requirements. The answer is not always simple. Geometries of the part to be manufactured will vary, as will the best-fit manufacturing technology. Technology choice will be affected not only by the type of metal being processed but also by its thickness, the required quality of cut and the speed at which the manufacturing operation needs to be completed.
Ultimately, however, there are some givens when it comes to process selection. Cost per part and quality are key and fairly universal drivers, and the customer is judge and jury when assessing the success of the manufacturing technology finally selected. This article explains why chemical etching is specified as the go-to technology by so many manufacturers.
Decisions
There are numerous metal cutting technologies available to OEMs, many of them very niche in their application and often unable to process a sufficiently wide array of materials or provide the accuracy and precision increasingly demanded by important industry sectors such as medical, aerospace, automotive, chemical and electronics.
When benchmarking technologies that are able to produce precision metal parts, the field is narrowed, the key players being universally recognised as stamping, punching, laser cutting and, to a lesser extent, chemical etching. Within the context of these alternatives, the unique characteristics of chemical etching overcome many of the issues associated with traditional metal cutting technologies and as such—in some instances—when looking for a cost-effective solution for the manufacture of precise metal parts, it is the only viable choice.
Starting at design
Before drilling down into the comparison between chemical etching and its traditional alternatives, a little time needs to be spent looking at design.
The best design in the world is only any good if it can be manufactured, and it is therefore up to the design engineer to ensure that the parts being designed are suited to the vagaries of the manufacturing process being employed. Ultimately, therefore, it is fair to say that the constraint on the level of innovation from the design side is the capabilities and often the limitations of the chosen manufacturing technology.
Once design engineers have selected chemical etching as their preferred metalworking process, it is important that they come to fully appreciate not only the technology’s versatility, but also the specific aspects of it that can affect—and in many instances enhance—product design.
Chemical etching possesses many attributes that can stimulate innovation and stretch the boundaries in terms of the inclusion of challenging product features, enhancements, complexity and efficiency, and it is important that design engineers fully exploit its potential.
Often, optimum success involves early-stage engagement with a chemical etching specialist. A partnership needs to be forged, not a customer subcontractor relationship, if the true potential of chemical etching is to be realised.
So, what are the key inherent characteristics of the chemical etching process that can be exploited at the design stage?
First off, it can be applied to a vast spectrum of metals in a variety of thicknesses (typically sub-1.5 mm), grades, tempers, and sheet sizes (up to 600 x 1,500 mm).
Next, it affords a high degree of accuracy, a key consideration for any design. Standard etching tolerances of ±10 percent of the metal thickness are possible, to a minimum of ±0.025 mm. Subject to development, greater accuracy can be realised, as can component features to sizes below the standard minimum.
Design engineers should also be made aware that due to the inherent edge, ‘cusp’ (figure 1), created during the process, unique characteristics can be designed into products. The etch cusp can be controlled and this enables a range of profiles to be introduced for the manufacture of sharp cutting edges such as those used in medical blades or conical openings such as those used to direct fluid flow in filtration meshes (figure 2).
Figure 1: Unique characteristics can be designed into products manufactured using chemical etching due to the inherent edge, ‘cusp’, created during the process.
Figure 2: The etch cusp can be controlled and thus introduce a range of profiles, allowing for the manufacture of sharp cutting edges or conical openings.
Chemical etching not only copes well with difficult geometries, but offers design engineers enormous flexibility, facilitating the adjustment of designs right up to the point of manufacture due to the use of digital tooling.
Manufacturing advantages and benchmarking
Chemical etching produces stress-free, flat components by selective etching through a photo-resist mask. It is especially well-suited to the manufacture of precision parts such as:
- grids and meshes;
- lead frames for integrated circuit boards;
- fuel cell and heat exchanger plates;
- precision springs;
- washers and gaskets; and
- aesthetic parts such as automotive interior trim.
Compared with traditional metal manufacturing technologies, chemical etching has a number of inherent advantages. For example, it is agnostic to metal choice. Metals suitable for etching can be both ferrous and non-ferrous, and include austenitic and martensitic steels, coppers, brass, and nickels. Hard to machine metals such as aluminium and titanium and its alloys as well as high-temperature alloys such as Inconel can be processed.
When looking at both of the conventional processing technologies, each suffers from a number of drawbacks, key among which is the degradation of the material being processed due to high impact or, in the case of laser cutting, the use of intense heat. In addition, traditional processes often leave burrs and require costly and time-consuming post-processing operations. As an ambient temperature, no contact machining process, chemical etching produces 100 percent burr- and stress-free parts.
Another crucial differentiator is in the area of tooling, which can be illustrated by comparing chemical etching with stamping. Tooling for chemical etching is digital, so there is no need to start cutting expensive and difficult to adapt steel moulds. This means that large quantities of products can be reproduced with absolutely zero tool wear, ensuring that the first and millionth part produced are precisely the same.
Also, as the tooling is digital, it can be adapted and changed extremely quickly and economically, enabling the design engineer to tweak designs right up to the eleventh hour and allowing for prototype up to high-volume production runs. This allows for design optimisation without financial penalty, helps ensure a low-risk entry strategy and facilitates easy product updating. Turnaround time using photo-tools is about 90 percent less than that for stamped parts. Stamping requires substantial investment in mould fabrication, which is not only costly but, in some instances, can take from six to ten months to complete, compared with a few hours for chemical etching.
The economy and adaptability of the tooling for chemical etching is a key stimulus to design freedom, along with the ability to produce what may seem impossibly complicated products. The cost of creating prototypes is low, and complex designs can be produced in a matter of days and design iterations in a few hours.
Today, an increasing number of OEMs from across all industrial sectors make products that are extremely complex and also very fragile. In many instances, geometric complexity and the requirement for extremely exacting tolerances and precision mean that chemical etching is not just a potentially desirable manufacturing process, but the only technology able to make certain products.
The complexity conundrum
When using stamping, part complexity more often than not adds cost, whether in low-, medium-, or high-volume applications. A complex product necessitates a complex mould tool, and complex tooling means increased costs, increased potential for tool failure and increased lead-times for satisfactory completion.
Chemical etching, on the other hand, is unaffected by the level of tool complexity, and it makes no difference in terms of cost or lead-time how complex the geometry of the part is and therefore the complexity of the digital tooling.
In addition, chemical etching has the ability to produce finer detail than stamping, with minimal if any degradation and deformation of the metal being processed and little to no likelihood of burrs or defects. Failure rates are minute, and unlike in the stamping process, every part produced is absolutely flat, which in some applications is absolutely vital.
Chemical etching’s sweet spot is the manufacture of complex parts in small- to medium-sized production runs. In extremely high-volume runs, where the tooling expense is justifiable and designs are not overly complex, stamping typically represents a more economic process.
Conclusion
The advantages of chemical etching over more traditional fabrication processes such as stamping and laser cutting are its low cost, high speed, flexibility, suitability for complex designs and ability to produce burr-free components, the properties of which are not changed by heat or stress.
Standard lead-times for chemical etching at Precision Micro are around one to two weeks, but they can be shorter to accommodate urgent demand. For stamping, it can take months just to design, build and de-bug a tool.
However, perhaps of greatest importance are the possibilities that are opened up to design engineers to innovate through the use of this versatile and cost-effective metal processing technology.
Precision Micro