How to polish a mold

Mold Polishing

For manufacturing a component of high surface finish and accuracy from an injection mold, it is essential to polish core and cavity of the mold so that the component can be easily ejected out after cooling without any scratch marks or deformation in the final component so that the finished product is of superior quality and pays well. Other advantages of mold polishing are reduced risk of local corrosion, fracture or cracking due to temporary overloading or pure fatigue. For molding transparent objects such as fiber lens or window for covers of electric meters, water bottles, injections used by doctors, mobile screens, etc. the core and cavity must be highly finished and so well polished that it reflects like a mirror. Though polishing is necessary, but it must not be over polished because it may deteriorate the shape of the cavity.

In some cases where mirror finish is not required then we can simply use high precision machines to produce well finished surfaces and save the expenditure in polishing-
Surface grinding machine
Cylindrical grinding machine
Lapping
Honing
Spark erosion
Die sinking
Pantograph
Reaming
CNC milling and lathe

If the surface finish from these operations is not sufficient then further polishing is required which is not a very easy process. Polishing demands high confidence and years of experience from the polisher and if the right tool and method is not adopted then howsoever experienced the polisher may be he can’t polish the surface adequately.

Rules for polishing operation
·        Dedicate a dust free room specially for polishing. Keep away all the chips and abrasive particles.
·        Polishing area should be very clean and moisture free. All the tools and accessories should be well arranged so that right tool can be selected as per requirement.
·        New wood and felt should not be used in between to avoid cross contamination of grit sizes.
·        Test every polishing stone on a scrap piece before polishing.

 Method of polishing
·        At first closely examine the mold surface and determine the fastest and most economical way to polish.
·        Inspect every high spot area and remove the material carefully with a cartridge wheel wrapped with an emery paper.
·        After this begin polishing with a wood with the help of polishing pate of soft stone mixed with the thinning oil. Any lubricating, non-corrosive mineral oil can be used as thinning oil.
·        Continue polishing with the harder stone further and diamond polish is the best for final polishing.
·        For having a mirror finish, further high grades of diamond polish are used subsequently ending at #1 grade diamond compound.

Polishing tips for mirror finish
·        An oil soluble diamond compound should be used.
·        A thinning oil which serves as lubricant is also used.
·        A vide variety wooden tools of balsa wood, hard wood, maple wood or brushes or felts are used as laps to develop the required finish.
·        Light pressure must be applied during diamond polishing.

After the polishing is complete, microscopic inspection is required to check for imperfections and scratches. The surface finish standards are often specified by SPI-SPE mold finish comparison kit. It consists of six steel disks polished to different levels. The surface roughness of the disks measured in RMS micro inches are described below.

Finishing number
Polishing techniques
Surface roughness
1
#3 Diamond polish
0.5 to 1.0
2
#15 Diamond polish
1.0 to 2.0
3
320 Grit Abrasive cloth
7.0 to 7.5
4
280 Grit Abrasive cloth
12.0 to 15.0
5
240 Grit Dry blast
26.0 to 32.0
6
24 Grit Dry blast
160.0 to 190.0

There are several defects that occur while polishing. Their knowledge is essential for successful polishing.
Orange Peel This defect occurs because of over polishing, the defective surface must be removed with hand with the stone with the grit size finer than the last grit used.
Pitting Due to high pressure of polishing, the hard non-metallic particles produce small pits in the surface. Light pressure must be applied and excess polishing should be avoided to eliminate this problem.


Comments

Post a Comment

Popular posts from this blog

The most Gruesome and filthy tortures invented in human history

Image
Most Brutal tortures in the history Impalement Invented in                                       -     Romania Time Taken by the victim to die   -     15 min to 3 days Brief description                             -     This was considered the most inhumane way of torture ever adopted in the history. For Impaling a victim, a tapered and oiled wooden stake is inserted inside the anus (in case of men) or in vagina (for women) from the pointed side. After this, it is stood in the vertical position so that the stake is inserted slowly with the own wait of the victim over a long period of time. The punishment was carried out until the stake comes out of the victim’s breast, shoulder, stomach or mouth. The cruelest part of this torture was that the pointed end was kept blunt enough to not kill the victim too early, so that he/she would have to endure the pain for several hours or even days before dying. The Judas cradle Invented in                                     
Read more

World's first analog computer

Image
Antikythera mechanism It is the oldest gear system found till date and is also famous as the oldest analog computer of the world. the calculator has been dated to be built in 1st century BC. The mechanism was found in 1900-1901 from a shipwreck off the coast of the Greek island of Antikythera and is of Greek origin. No other older artifact showing so much complex mechanism was ever found after that, hence Antikythera mechanism is of great historical significance. Reconstruction of Antikythera mechanism at Archaeological museum Athens It is actually a date calculator which was used as a calendar. The calculator had a small hand crank which is lost now. The hand crank was used to set the date and was linked to the largest gear through a crown gear. When the hand crank was rotated, all the gears inside were also rotated with it and various astronomical figures like position of the Sun, Moon phases, planets and eclipse cycles were calculated. The mechanism was made with
Read more

Most Evil Men and Women in the History

Image
25 Real Monsters Though, it seems irrelevant to prepare such a small list of monsters in the long history of world, since the toll still continues with an increased rate. Still I have tried to do so by picking some deadliest people of history, who had an appetite for torturing and killing people. These mass murderers were so evil that they were considered punishment from god, whose death became a day of celebration for most of the population of the world. The purpose of this list is to shake you if you are sad about your condition. At the end of this list, you’ll know that you still have a lot to be happy and celebrate. Queen Mary I Years Active       -     July 1553 to November 1558 Gender                -     Female Place                    -     London Nicknamed as    -     Bloody Mary She was               -     The Queen of England & Ireland Known For         -     She was a sadist ruler who was dissatisfied for all her life. During her rule, she
Read more