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Manufacturing Methodologies

There are many different techniques that can be used to manufacture a razor. This article details some of the terms and techniques that come up when discussing razors.

Tolerances

First off, a tolerance is just the amount of variation possible from one manufactured part to another. Think of it as "accuracy." If I'm hand-carving a part out of wood, each one is going to be a little different than the one before it, no matter how hard I try to make them the same. Low tolerances aren't necessarily a bad thing. If I'm hand-carving a fine pipe, it's not too big a deal of one is 0.5mm longer than the next. In fact, this uniqueness is often desired. But if I'm making a pressure valve for the space shuttle fuel tank, and it's is off by 0.001mm, things could get all explodey. If I'm making an artificial knee for a patient out of titanium, and I'm off by just a litte, that person might end up living in pain for the rest of their lives.

In regards to a razor, tolerances matter quite a bit. Someone above noted that you can't feel a difference of 0.1mm on your face. While that's true, that small difference could make a huge difference in the shape or angle of the blade. It could also significantly affect how the top and bottom fit together, and thus have a drastic effect on how much blood you get to keep in your face.

Methods

Casting

Casting, or more specifically gravity casting, is just the process of pouring molten liquid into a negative cavity and allowing it to harden. One really important thing I've read that few people seem to be aware of, though, is that when the material cools and hardens, it shrinks, (or sometimes expands) and deforms from the shape of the original mold. Different materials deform by different amounts and in different ways. I think this is incredibly important when it comes to the manufacture of razors, because when the engineers design a mold, they take this shrinkage into account, but can't always perfectly predict what's going to happen to the soft, cooling metal as it pulls away from the walls of the mold. This is one of the reasons that Zamak is so popular with manufacturers, because it shrinks very little, (<1%) and very predictably. Aluminum, on the other hand, can shrink as much as 6.5%, so is much more difficult to cast accurately. Because of this shrinkage, there is going to be some inherent inconsistency from one part to another, and that is one of the things that people talk about when they mention tolerances. Also, as the molds continually expand and contract as a result of the heating process, they also deform over time. This can cause changes in how the parts fit together, and can cause metal to seep out of the seams in the parts of the mold. (known as flashing.) Some companies haven't replaced or re-tooled their dies in decades, and this becomes very apparent in observed variances and general sloppiness in the finished products.

Sintering

Sintering is very similar to casting, in that a shapeless powder is put into a mold and heated, causing the powder molecules to adhere very tightly to one another. Note, they do not melt. It's a chemical reaction caused by heat and pressure. That pressure is an important part of the equation, because the pressure can also cause the original shape to deform, even more so than casting. However, this is taken into consideration when designing a part, so the end effect can actually be a more stable and predictable shape than gravity casting. On the other hand, there are limitations to the shapes that sintering can produce, since the mold actually must apply pressure during the shaping process. The end result should be a more consistent shape to the final product. However, this process can also fall victim to the same pitfalls as traditional casting. The dies making the products must be properly maintained, so they don't warp over the years. And if not monitored carefully, shoddy products can result. I believe the "waviness" in some Weber heads mentioned earlier in this thread is a perfect example of this. Since there haven't been sintered razor heads around for decades, it remains to be seen how the process will hold up over time. Re-tooling or re-creating a sintering mold is much more expensive than re-tooling a gravity cast mold, so only time will tell how these manufacturers maintain their standards.

MIM (Metal Injection Molding)

I know very little about MIM, apart from the Wikipedia article, so my only comment would be that it has the potential to produce relatively cheap metal parts at a high rate. It is essentially a method of casting, but rather than using gravity to feed the metal, it is injection molded. In theory, this could allow for molds to be produced much more cheaply, and the processes to manufacture could be done much more quickly and in a more automated fashion. (i.e. less expensive human intervention.) It would seem to me that it could have the same drawbacks as gravity casting, because you're still putting a hot liquid into a metal mold and cooling it into a solid, but honestly, I don't know how well it holds up in that regard. It's a fairly new process, and as of this writing, there are no razors on the market that use this technique for manufacturing. Typically, this process is seen it in the context of "faster/cheaper" rather than higher quality.

Stamping or Rolling

Stamping and/or rolling are basically the same from a design standpoint. Rather than start with a liquid or powder, this process starts with a solid uniform sheet of metal. That metal is fed into a roller or press which can apply dozens or even thousands of tons of force, which can punch holes and deform the metal. It can result in very tight tolerances, since there is no melting or cooling to account for. It's also very cheap to do in large quantities, and can be done very, very quickly. Almost all vintage Gillette razors were made this way, except for a few New Standard and New Deluxe models made in the 1930's. The main disadvantage of this process is that you are very constricted in the design of the part. Since the metal starts as uniform thickness, you can't make a thick, chunky part, or a part that isn't more or less a uniform thickness. If you look at the Gillette Tech, for example, Gillette worked around this limitation by pressing a diamond pattern into the baseplate to give it greater rigidity and the characteristics of a thicker razor. But the metal itself is still the same actual thickness through the whole baseplate.

Machining or CNC Milling

Which brings us to machining or milling. More specifically, in the case of razor heads, I'm referring to CNC milling. Technically, turning metal on a lathe (as in the case of a razor handle) is also machining, but it's a much simpler and less expensive process, and pretty much limited to round or cylindrical shapes. CNC milling is capable of producing incredibly accurate and consistent parts. Almost all parts that require a high tolerance. Airplane parts, medical implants and prosthesis, firearms, high accuracy industrial valves, etc. are almost all exclusively made by CNC milling. Most materials can be CNC milled, and the process can produce almost any shape imaginable. It's a subtractive process, so you start with a block of whatever material you are milling and subtract the parts you don't want to end up with the final shape. Since it's done by a computer/robot arm, it can be incredibly accurate and consistent from one part to the next. Since there is no heat up/cool down in the process, you don't need to worry about shrinkage of the part. It is the modern gold standard for manufacturing, but it's not without its downsides.

First and foremost, the machines are incredibly expensive, and require an expert to operate. The operator needs to know how to program in the three dimensional shapes, but at the same time, needs to know a lot of the materials science about the materials he or she is cutting. Since you start with more material, then cut pieces of it away, there is a significant amount material lost in the process, usually more than the amount in the final piece. Not only are the machines expensive to purchase, they are expensive to maintain. Depending on the hardness of the material you are cutting into, you have to replace the bits fairly often. If the operator isn't well versed on the materials being cut, they can (and often do) break the bits, or even the entire machine. Finally, it's the slowest of all of the processes. Even though the robot arms can move incredibly quickly, the speed at which they cut into the metal can't be rushed. Go too fast, and you risk damaging the milling bit, the machine, the part, or all three. Parts must machined one at a time, so the process doesn't scale at all. The cost to manufacture one part is more or less the same, regardless of whether you need ten or ten thousand. Something like a razor head might take 30-90 minutes to machine for each part. Assuming, say, 60 minutes per part, and allowing for some defects, a single CNC machine can't physically make more than 1500 - 2000 in a year, and that's assuming that machine makes nothing but that same razor for 40 hours per week, 52 weeks per year. You could, of course, spread the job around to several machine shops, but then you have to make sure each product meets the same tolerances and whatever standards you have set for your product.

This is another illustration of how important tolerances can be. Inexpensive CNC machines can make quick, rough cuts, but there will be a lot of variability between parts. On the other hand, extremely expensive machines with high end tooling, make very small, slow cuts, and get a much higher tolerance. Depending on the tolerances required the cost of machining can vary a lot. The higher tolerances require more expensive machines and tooling, and probably a more experienced (read: more expensive) machinist. If you do spread out the manufacture, you need to make sure each and every shop is using the same plans, the same tooling, and cutting to the same tolerances. All of this contributes significantly to the expense of machined razor heads.

See also


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