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FAQ
Frequently Asked Questions Regarding PVD, CVD
& TD coating
1.
What is PVD coating?
Physical Vapor Deposition, or PVD, is a term used to describe
a family of thin-film coating processes which are applied under
vacuum conditions (10-2 to 10-4 Torr). These processes involve
the generation of positively charged ions of various metals. These
metal ions react with gas ions that are introduced into the chamber
in order to create various compositions. The parts to be coated
are given a negative bias in order to attract the positively charged
ions. The result is a very strong mechanical bond between the
coating and the tool.
Recently,
numerous improvements have been introduced within the PVD coating
industry, and Richter Precision Inc. has been leading the way.
We have developed new coating compositions, new multi-layer
combinations, a family of DLC coating processes, and new technological
advancements such as Filtered Arc technology and improved etching
processes. We are devoted towards maintaining our position as
a leader in PVD coating technology.
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2.
What is CVD coating?
Chemical Vapor Deposition, or CVD, is a thin-film coating with a
diffusion type bond that results from the reaction between various
gaseous phases and the heated surface of a substrate. The final
product is a hard, wear-resistant coating with an extremely strong
bond to the substrate. CVD is sometimes referred to as a “hot
coating” because the process approaches temperatures around
1900°F. For this reason, special post-coating vacuum heat-treating
processes have been developed for tool steel components.
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3.
What is TD coating?
Thermoreactive Diffusion (TD or TRD) is a high temperature, multi-stage
coating process for producing metal carbides (typically vanadium
carbide) on the surface of carbon-containing substrates. These coatings
exhibit a diffusion type bond with the substrate, thereby providing
very high adhesion between the metal carbide layer and the base
metal. This bonding characteristic, combined with the coating’s
extremely high hardness, translates into excellent resistance to
the types of wear and galling typically seen in many metal-forming
applications.
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4.
Why should I use PVD, CVD and/or TD coatings?
Regardless of the tooling application, the primary reason for
using these coatings is very simple: to lower your cost-per-part.
Our customers consistently experience longer tool life while also
being able to operate at increased speeds and feeds. The savings
calculation becomes very easy: reduced down-time for PM and/or
tool changes + increased production rates = significant and tangible
savings for your company.
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5.
How do PVD, CVD and TD coatings improve tool life and performance?
Although all of our various coatings have some variation in their
properties in order to augment their performance in specific applications,
there are two main properties that are fundamental to all of our
coatings: high hardness and lubricity.
The average
relative micro-hardness of our PVD, CVD, and TD coatings would
be well over 80 Rc. When this hardness is compared to 58-62 Rc
of tool steel, 62-65 Rc of HSS, or 70-76 Rc of carbide, one gets
a clearer picture of the comparative hardness of our coatings.
This higher hardness gives cutting tools, forming tools, and wear
components much greater protection against abrasive wear.
As for lubricity,
the Coefficient of Friction of our coatings can be significantly
lower than un-coated tool substrates. For forming tools, this
low Coefficient of Friction means that tools work with less force
due to reduced resistance. In cutting applications, reduced friction
means less heat is generated during the machining process, thereby
slowing the breakdown of the cutting edge. In slide wear applications,
the coatings greatly reduce the tendency of materials to adhere:
this reduces friction and allows for more unrestricted movement.
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6.
How much of an increase in tool life should be expected after PVD,
CVD or TD coating?
Conservative estimates would range from 2-3 times the life of
an un-coated tool; however, many applications have shown increases
in tool life that exceed 10 times that of an un-coated tool. When
a customer works with our experienced staff to match the appropriate
coating with their substrate and application, dramatic improvement
is the resulting outcome.
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7.
Which coating process is best for my application?
There are many variables that must be calculated when considering
this question, such as application, substrate, and tool tolerances.
The simple answer is that when the tolerances and materials allow,
CVD coating has proven to be superior in many applications, especially
in high stress metal-forming applications where “sliding friction
wear-out” and galling are pervasive. The CVD process creates a
diffusion type bond between the coating and the substrate which
is much stronger than the bond created through the PVD process.
A potential area for concern with CVD coating is the 1900°F process
temperature. This characteristic can limit CVD coating in some
applications.
The PVD coating process has been successful in a wider range of
substrates and applications. This success is largely due to its
lower process temperatures (200°F-750°F) and average coating thicknesses
of 2-5 microns. These characteristics, among others, make PVD coatings
ideal for HSS and carbide cutting tools (no excessive coating build-up
on cutting edges) as well as parts with tight tolerances such as
plastic injection molding components and fine blanking tools. In
addition, the lower process temperatures mean zero distortion will
be observed on most materials, as long as proper draw temperatures
are maintained.
Please contact Richter Precision Inc. if you have further questions
regarding differences between PVD and CVD coatings. In addition,
please reference the “Comparison of Coating Processes” page of this
website.
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8.
Is it possible to mask certain areas on parts to prevent them from
being coated?
PVD is a line-of-sight process; therefore, it is possible to mask
areas in order to prevent them from receiving coating deposits.
When custom masking fixtures are required, our in-house machine
shop is able to respond quickly in order to meet the customer’s
needs.
The CVD process
uses various gases during the coating process; therefore, coating
will deposit anywhere the gas can contact the substrate. Due to
the nature of this process, post-coating grinding of critical
dimensions using a diamond wheel is usually a better option.
The TD process
uses a molten salt bath during the coating process; therefore,
coating will deposit anywhere the liquid can contact the substrate.
Due to the nature of this process, post-coating grinding of critical
dimensions using a diamond wheel is usually a better option.
Please contact
us regarding feasibility and costs related to masking your particular
application.
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Please contact
us regarding feasibility and costs related to masking your
particular application.
9.
What is the average thickness of your coatings?
The average thickness of our various PVD coatings is 2-5 microns
(.00008-.0002”). The average thickness of our various CVD
coatings is 5-10 microns (.0002-.0004”). The average thickness
of our TD coating is 4-15 microns (.00016-.0006”).
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10.
What are the processing temperatures for PVD, CVD and TD coatings?
The process temperatures for our PVD coatings can range from 200°F-750°F
depending upon the particular coating being deposited. Please note
that we recommend draw temperatures of 750°F+ in order to avoid
distortion or hardness changes. If these draw temperatures are not
possible for your parts, then we recommend you contact us for special
instructions in order to provide for the safe processing of your
parts.
The process
temperature for CVD coating will reach 1925°F; therefore,
any tool steels or HSS being CVD coated will be annealed during
coating. After coating, we will vacuum heat-treat all steels in
order to achieve the customer’s required hardness.
The process
temperature for TD coating will generally be about 1650°F;
therefore, any tool steels or HSS being TD coated will be annealed
or partially annealed during coating. After coating, we will vacuum
heat-treat all steels in order to achieve the customer’s
required hardness.
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11.
What materials are suitable for PVD, CVD and TD coating processes?
High Speed Steels, carbides, and a wide variety of tool steels are
among the most commonly coated materials for both these processes.
A more detailed list is available by accessing the “Material/Coating
Compatibility” page of this website.
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12.
What are the average turn around times for your coating processes?
The average turn around time for PVD coatings range from 2-5
working days, depending upon the specific coating composition. The
average turn-around time for CVD coatings is about 5-7 working days.
The average turn-around time for TD coating is about 5 working days.
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13.
Are you able to remove your PVD, CVD and TD coatings?
We have de-coating processes available for removing all of our coatings.
These processes remove only the coating layers while not affecting
a majority of tool substrates. Contact your Richter Precision, Inc.
representative for more information.
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