U.S. patent application number 13/480468 was filed with the patent office on 2013-11-28 for metal injection molding method.
This patent application is currently assigned to Cheng Uei Precision Industry Co., LTD.. The applicant listed for this patent is Te-Chang Chen, CHIH-WEI CHENG, Cheng-Yu Chou. Invention is credited to Te-Chang Chen, CHIH-WEI CHENG, Cheng-Yu Chou.
Application Number | 20130315774 13/480468 |
Document ID | / |
Family ID | 49621755 |
Filed Date | 2013-11-28 |
United States Patent
Application |
20130315774 |
Kind Code |
A1 |
CHENG; CHIH-WEI ; et
al. |
November 28, 2013 |
METAL INJECTION MOLDING METHOD
Abstract
The present invention discloses a metal injection molding
method, which is adapted to a mold having multiple mold cavities,
and includes a feedstock preparation step, a molded articles
ejection step, a classification and management step, a wax-based
material removal step, a sintering step, and a compacting step. The
classification and management step is to classify molded articles
according to differences of the molded articles. The sintering step
is to sinter the molded articles with sintering parameters. In this
manner, tolerance caused by injection molding process is reduced
because of the classification and management step and the sintering
step, whereby further improving productive rate and quality of
products produced from the mold with multiple mold cavities.
Inventors: |
CHENG; CHIH-WEI; (New Taipei
City, TW) ; Chou; Cheng-Yu; (New Taipei City, TW)
; Chen; Te-Chang; (New Taipei City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CHENG; CHIH-WEI
Chou; Cheng-Yu
Chen; Te-Chang |
New Taipei City
New Taipei City
New Taipei City |
|
TW
TW
TW |
|
|
Assignee: |
Cheng Uei Precision Industry Co.,
LTD.
New Taipei City
TW
|
Family ID: |
49621755 |
Appl. No.: |
13/480468 |
Filed: |
May 24, 2012 |
Current U.S.
Class: |
419/28 |
Current CPC
Class: |
B22F 2998/10 20130101;
B22F 3/02 20130101; B22F 3/1021 20130101; B22F 3/225 20130101; B22F
3/10 20130101; B22F 3/225 20130101; B22F 2998/10 20130101 |
Class at
Publication: |
419/28 |
International
Class: |
B22F 3/24 20060101
B22F003/24 |
Claims
1. A metal injection molding method, adapted to a mold with
multiple mold cavities, comprising: a feedstock preparation step
for mixing metal powder and a binder to produce a feedstock; a
molded articles ejection step for injecting the feedstock into the
multiple cavities of the mold so as to shape the feedstock as
multiple molded articles, and then ejecting the molded articles
from the mold; a classification and management step for
individually managing and classifying the multiple molded articles
according to differences among the multiple molded articles; a
wax-based material removal step for cleaning the molded articles
with solvents or heating the molded articles to remove the binder;
a sintering step for sintering the multiple molded articles with
sintering parameters where the multiple molded articles are placed
in a sintering chamber according to classifications of the multiple
molded articles; and a compacting step for compacting the multiple
molded articles after being sintered so as to produce end
products.
2. The metal injection molding method of claim 1, wherein the
differences among the multiple molded articles in the
classification and management step include dimensional difference,
surface difference, or different mold cavities.
3. The metal injection molding method of claim 1, wherein in the
classification and management step the multiple molded articles are
classified according to each of the mold cavities.
4. The metal injection molding method of claim 1, wherein in the
sintering step the molded articles are being sintered with
different sintering parameters according to different
classifications of the multiple molded articles.
5. The metal injection molding method of claim 1, wherein in the
sintering step the molded articles are being sintered with the same
sintering parameters.
6. The metal injection molding method of claim 1, wherein the
sintering parameters are set to control a temperature, time,
pressure, and atmosphere during sintering.
7. The metal injection molding method of claim 1, wherein after
being classified the molded articles of larger size are placed at
peripheral portions of the sintering chamber, and the molded
articles of smaller size are placed at a middle portion of the
sintering chamber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an injection molding
method, and particularly to a metal injection molding method
adapted to a mold with multiple cavities for reducing tolerance and
producing high precision products.
[0003] 2. Related Art
[0004] In brief, a process of metal powder injection molding (MIM)
includes steps of preparing a feedstock for being fed into a
plastic molding machine to be shaped, then cleaning with solvents
or heating the shaped article to remove wax-based materials, then
sintering the shaped article in a sintering furnace to remove all
the other binders, and compacting the metal powder at last.
[0005] Electronic products today have extremely small parts inside
and are fabricated in relatively high precision. Thus dimensional
tolerance is required to be as small as a nearly zero dimensional
difference among products. Traditionally, an injection mold is
provided with one mold cavity in order to effectively control the
product dimension. However, it is not preferable to mass produce
through one mold with one cavity because of a lower production
rate. As a result, one mold with multiple cavities has been
designed to produce multiple same products at a time by one
injection molding. Although one mold with multiple cavities can
increase the production volume, it is also affected by more
variables during the molding process. For instance, the gravity
acceleration probably will cause the feedstock material to flow in
different speeds into different mold cavities, and whether surfaces
of flowing channels are smooth or tough influences material flow
property as well, whereby leading to a visible dimensional
tolerance between products.
[0006] Additionally, referring to FIG. 1, a traditional sintering
furnace 9 has a chamber 92 typically surrounded by a plurality of
heating elements 91. Numerous articles 93 are put in the chamber 92
to undergo a process of sintering including heating, holding time,
cooling and other steps so as to produce metal components. However,
articles 93 molded from a traditional mold with multiple cavities
are placed disorderly in the chamber 92 in a manner such that
articles from a same cavity are spread randomly in the chamber 92
(as shown in FIG. 1). As a result, articles from the same cavity
are kept different distance from the heating elements 91 to each
other. However, distance between the heating elements 91 and
articles is known to significantly influence heating efficiency no
matter it is heated through thermal radiation, thermal convection,
thermal conduction or other methods. Different distance between
articles and heating elements, different heating efficiency, and
dimensional tolerance all result in remarkable dimensional
differences of end products which are certainly not qualified to
meet requirements.
SUMMARY OF THE INVENTION
[0007] Accordingly, an object of the present invention is to
provide a metal injection molding method adapted to a mold with
multiple mold cavities, utilizing classification of molded articles
and setting of sintering parameters to improve productive rate and
produce high precision products.
[0008] To achieve the above-mentioned objects, the metal injection
molding method, adapted to a mold with multiple mold cavities,
comprises: a feedstock preparation step for mixing metal powder and
a binder to produce a feedstock; a molded articles ejection step
for injecting the feedstock into the multiple cavities of the mold
so as to shape the feedstock as multiple molded articles, and then
ejecting the molded articles from the mold; a classification and
management step for individually managing and classifying the
multiple molded articles according to differences among the
multiple molded articles; a wax-based material removal step for
cleaning the molded articles with solvents or heating the molded
articles to remove the binder; a sintering step for sintering the
multiple molded articles with sintering parameters where the
multiple molded articles are placed in a sintering chamber
according to classifications of the multiple molded articles; and a
compacting step for compacting the multiple molded articles after
being sintered so as to produce end products.
[0009] With the above-mentioned method, tolerance caused by
injection molding process is reduced because of the classification
and management step and the sintering step, whereby further
improving productive rate and quality of products produced from the
mold with multiple mold cavities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic cutaway view showing a sintering
chamber stored with multiple articles of prior art;
[0011] FIG. 2 is a schematic top plan view of a mold with multiple
mold cavities of a metal injection molding method of the present
invention;
[0012] FIG. 3 is a detailed flowchart of the metal injection
molding method of the present invention; and
[0013] FIG. 4 is a schematic cutaway view showing a sintering
chamber stored with multiple articles according to classifications
of the multiple articles of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Referring to FIG. 3 illustrating a detailed flowchart of a
metal injection molding method 100 in accordance with the present
invention, the process 100 is adapted to a mold 7 with multiple
mold cavities 70 (as shown in FIG. 2) and to produce high precision
metal parts. In this preferable embodiment, the mold 7 has four
corresponding mold cavities 70. The metal injection molding method
100 comprises a feedstock preparation step 1, a molded articles
ejection step 2, a classification and management step 3, a
wax-based material removal step 4, a sintering step 5, and a
compacting step 6.
[0015] The feedstock preparation step 1 is intended to prepare a
feed stock by mixing metal powder and a binder.
[0016] The molded articles ejection step 2 is intended to produce
multiple molded articles 71, 72, 73, 74 (also referred to green
part) by injecting the feedstock into the multiple cavities 70 of
the mold 7 so as to shape the feedstock, and then eject the shaped
feedstock as the molded articles 71, 72, 73, 74 from the mold
7.
[0017] The classification and management step 3 is intended to
individually manage the multiple molded articles 71, 72, 73, 74 so
as to classify them according to differences among the multiple
molded articles 71, 72, 73, 74.
[0018] The wax-based material removal step 4 is intended to remove
the binder by cleaning the molded articles 71, 72, 73, 74 with
solvents or heating the molded articles 71, 72, 73, 74.
[0019] The sintering step 5 is intended to form sintered articles
(also referred to brown part) by sintering the multiple molded
articles 71, 72, 73, 74 with sintering parameters where the
multiple molded articles 71, 72, 73, 74 are placed in a sintering
chamber 81 according to classifications of the molded articles 71,
72, 73, 74.
[0020] The compacting step 6 is intended to compact the sintered
articles 71, 72, 73, 74 so as to produce end products.
[0021] Particularly, the differences among the multiple molded
articles 71, 72, 73, 74 in the classification and management step 3
include dimensional difference, surface difference, different mold
cavities 70 or any other differences. Such differences are capable
of being distinguished by eyes or hands or instruments.
Classifications of the molded articles 71, 72, 73, 74 are
determined according to such differences. For example, when
classified according to the four mold cavities 70, the molded
articles 71, 72, 73, 74 are classified into four classifications,
each one of the mold cavities 70 representing one classification.
The multiple molded articles 71, 72, 73, 74 are placed in the
sintering chamber 81 respectively according to their
classifications so as to be sintered with the sintering parameters
at high temperature.
[0022] The sintering parameters are set to control a temperature,
time, pressure, and atmosphere during sintering, and may be varied
according to classifications of molded articles. One of the
embodiments of sintering is that molded articles from the same mold
cavity are being sintered together at a time, while other molded
articles from other mold cavities are being sintered separately
with different parameters. Another embodiment of sintering is that
different classifications of molded articles are being sintered
with different parameters. Alternatively, different classifications
of molded articles are capable of being sintered with same
parameters, wherein further changes of the molded articles resulted
from the process of sintering are capable of counterbalancing
tolerance resulted from the process of injection molding.
Furthermore, a secondary processing step is able to be performed
after the compacting step 6, such as electroplating, polishing, or
sandblasting.
[0023] Referring to FIG. 4 illustrating an embodiment of the molded
articles 71, 72, 73, 74 that are placed in the sintering chamber
81, in the classification and management step 3 the molded articles
71, 72, 73, 74 are classified according to their dimensional
difference. In this embodiment, the molded articles 71 of larger
size are placed at peripheral portions of the sintering chamber 81
in order to be close to the heating elements 82 to improve a
heating efficiency. The molded articles 74 of smaller size are
placed at a middle portion of the sintering chamber 81 where the
heating elements 82 are further away from the molded articles 74
causing a lower heating efficiency. As a result, during the process
of sintering, tolerance, caused by injection molding, of both the
molded articles 71 of larger size and the molded articles 74 of
smaller size is reduced because of different heating efficiency. In
other words, after being sintered the molded articles 71 of larger
size will become smaller whereby to ensure that each molded article
from the same mold has almost the same dimension and to achieve the
purpose of mass-produced by one mold with multiple mold
cavities.
[0024] Accordingly, the present invention utilizes the
classification and management step 3 to preliminarily classify the
green parts so as to place the green parts appropriately in the
sintering chamber 81 according to different classifications.
Furthermore, the sintering step 5 is performed to set the sintering
parameters in order to reduce tolerance caused by injection molding
to improve the productive rate and yield rate of the metal
injection molding method adapted to one mold with multiple mold
cavities, whereby achieving the purpose of mass production of high
precision products and greatly reducing the number of unqualified
products, so as to effectively control the cost of
manufacturing.
[0025] It is understood that the invention may be embodied in other
forms within the scope of the claims. Thus the present examples and
embodiments are to be considered in all respects as illustrative,
and not restrictive, of the invention defined by the claims.
* * * * *