Low Pressure Injection Moulding enables production of large parts

 

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Cordially

Amelia
B2B Marketing and Social Networking
CN Mould & Plastic Limited  (Video: http://www.youtube.com/watch?v=u2lgkSbNNkg )
Add: CN Hi-Tech industry park, No.227, Xiangshan Rd., Luotian 3rd industry zone, Songgang, Baoan, Shenzhen, 518105, China.
Tel: 86-755-86060383, 86061383, 86060363  Ext:828
Fax: 86-755-86060393
Skype: niya2000007
MSN : cntsales@live.cn
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Injection Molding Cycle Time

Cycle Time,

 

is the time required to close a mold, inject the material, cool the material, open the mold, eject the part, and, in the case of inserts, reset the mold.

 

Cycle times can be made faster by having well-designed parts with walls that maintain a uniform thickness and which are no thicker than necessary. Thick-walled parts take longer to cool due to the extra material and slow down cycle times.

 

On a per part basis, cycle times can be greatly improved by adding additional cavities to the molds. By using multi-cavity molds one cycle can produce several parts instead of just one in the same amount of time.

 

 

 

 

 

 

Cordially

 

Amelia
B2B Marketing and Social Networking
CN Mould & Plastic Limited  (Video: http://www.youtube.com/watch?v=u2lgkSbNNkg )
Add: CN Hi-Tech industry park, No.227, Xiangshan Rd., Luotian 3rd industry zone, Songgang, Baoan, Shenzhen, 518105, China.
Tel: 86-755-86060383, 86061383, 86060363  Ext:828
Fax: 86-755-86060393
Skype: niya2000007
MSN : sales@cnmouldplas.com
Website: www.cnmouldplas.com

 

Injection Molded Parts Design–by Elito

Injection molded parts are made of thermoplastics, a polymer that turns into liquid when heated then turns back to solid when cooled.

Carefull thoughts on the following elements shall be considered for the design of plastic injection molded part.

Wall Thickness

As much as possible use a uniform wall thickness. If you must change the wall thickness, change it gradually to avoid warping.

If the strength is not compromised, design the part with minimal wall thickness to allow faster cooling time and cycle time.

Draft angles

Draft angle is necessary for easy removal of molded part from the mold. Draft angle should be applied in the direction of draw from the cavity and core.

Parts with textured surface require greater draft angle in order to avoid scratches on the textured surface as the part is being removed from the mold. 1 to 3 degrees normally applies to moderately matte or sand-blasted surfaces and 3 to 5 degrees for roucher surface.

But for smaller precision molded parts, it is sometime unnecessary to include draft angles as long as the cavity and core are highly polished.

Corner Radius

Apply radius on corners as much as possible. A proper radius size is not less than the wall thickness of the part.

Radius reduces the stress on the corner thus reducing the warpage compared to corners without radius.

Rib

Apply rib instead of using thicker wall thickness. Uneven cooling of thick wall will lead to uneven shrinkage inside and outside the wall. This could cause warpage and sinkmark due to internal stress. Applying rib will help improve the rigidity and geometric integrity of the molded part. It also improves the cooling time.

Mold Standards

Molders and Moldmakers can build a mold in a wide variety of ways – ranging from the quick & economical prototype mold to the super high quality, long lasting production mold.  The problem is in making sure that when a mold is quoted everyone involved is “on the same page”.Detailed Mold designs featuring a full Bill of Materials, Assembly drawings, and Detail drawings.

A-Series DME Standard Mold Bases, #2 Steel (28-30R/C).

Cavity & Core Machined in P-20 Steel Inserts (30-32 R/C) [However, about 50% of the molds we build utilize hardened H-13, S-7, or 420SS (48-58 R/C).  We try to recommend core & cavity materials based upon what we know about the project - part material, production amounts, life of the program, cycle requirements, expected maintenance, etc.]

SPI #3 Cavity Finish.

Water/Cooling lines in Cores and Cavities (and in sub-inserts & slide bodies if feasible) with connectors.

Guided Ejection system with Spring Loaded Return & Tapped Knock-out holes.

Lifters typically have a Core and a separate lifting rods, Lifter guide bushings, and replaceable gib/couplings.

Tunnel (sub) gate if possible (Edge/Chisel gate if Tunnel gate is not feasible).

Hot Runner Systems are typically built in-house with Standard DME components OR purchased from a recomended hot runner supplier.

Mold is stamped with Customer Name, Part Name, Part Number, Approximate Weight, and Manufacture Date.  Inserts and Details are stamped with Material type and Detail Number.

 

Also, we try to recommend Parting Line Locks, Switches, Early Ejector Return Systems, Accelerated Ejectors, as well as other components and peripherals when we believe they are necessary.

 

SPI: MOLD CLASSIFICATIONS

INTRODUCTION

 

The following classifications are guidelines to be used in obtaining quotations and placing orders for uniform types of molds. It is our desire through these classifications to help eliminate confusion in the mold quote system and increase customer satisfaction. It is strongly recommended that mold drawings be obtained before construction is started on any injection mold. Even though parts may seem simple enough not to warrant a mold design, a drawing showing sizes and steel types will pay for itself in event of mold damage. These classifications are for mold specifications only and in no way guarantee workmanship.

It is very important that purchasers deal with vendors whose workmanship standards and reliability are well proven.

 

Mold life, because of variations in part design and mold conditions, cannot be guaranteed. This guide will attempt to give approximate cycles for each type of mold excluding wear caused by material abrasion, poor mold maintenance and improper molding technique. Maintenance is not the responsibility of the moldmaker. Normal maintenance such as replacement of broken springs, broken ejector pins, worn rings, or the rework of nicks and scratches should be borne by the molder. Mold rework costs should be closely considered when deciding which classification of mold is required. This document does not constitute a warranty or guarantee by the Society of the Plastics Industry, Inc., or its members for the classifications or specifications set forth herein.

 

CLASSIFICATION OF INJECTION MOLDS UP TO 400 TONS

 

The following contains a brief synopsis of the various mold classifications and the detailed descriptions of each mold class. Again, it is our recommendation that a MOLD DATA SHEET (an example of which is in the back of the SPI manual) be included with each request for quotation.

 

GENERAL SPECIFICATIONS

 

1. Customer to approve mold design prior to start of construction.

2. All molds, with the exception of prototype, to have adequate channels for temperature control.

3. Wherever feasible, all details should be marked with steel type and Rockwell hardness approximately .005 deep.

4. Customer name, part number, and mold number should be steel stamped on mold.

5. All molds should have eyebolt holes on the top side. There should be one above and one below the parting line to facilitate mold removal, if required, in halves.

 

CLASS 101 MOLD

 

Cycles: One million or more

Description: Built for extremely high production. This is the highest priced mold and is made with only the highest quality materials.

Detailed mold design required.

Mold base to be minimum hardness of 28 R/C.

Molding surfaces (cavities and cores) must be hardened to a minimum of 48 R/C range. All other details, such as sub-inserts, slides, heel blocks, gibs, wedge blocks, lifters, etc. should also be of hardened tool steels.

Ejection should be guided.

Slides must have wear plates.

Temperature control provisions to be in cavities, cores and slide cores wherever possible.

Over the life of a mold, corrosion in the cooling channels decreases cooling efficiency thus degrading part quality and increasing cycle time. It is therefore recommended that plates or inserts containing cooling channels be of a corrosive resistant material or treated to prevent corrosion.

Parting line locks are required on all molds.

 

CLASS 102 MOLD

 

Cycles: Not exceeding one million

Description: Medium to high production mold, good for abrasive materials and/or parts requiring close tolerances. This is a high quality, fairly high priced mold.

Detailed mold design required.

Mold base to be minimum hardness of 28 R/C.

Molding surfaces should be hardened to a 48 R/C range. All other functional details should be made and heat treated.

Temperature control provisions to be directly in the cavities, cores, and slide cores wherever possible.

Parting line locks are recommended for all molds.

The following items may or may not be required depending on the ultimate production quantities anticipated. It is recommended that those items desired be made a firm requirement for quoting purposes:

a. Guided Ejection

b. Slide Wear Plates

c. Corrosive Resistant Temperature Control Channels

d. Plated Cavities

 

CLASS 103 MOLD

 

*Cycles: Under 500,000

Description: Medium production mold. This is a very popular mold for low to medium production needs. Most common price range.

Detailed mold design recommended.

Mold base must be minimum hardness of 8 R/C.

Cavity and cores must be 28 R/C or higher.

All other extras are optional.

 

CLASS 104 MOLD

 

*Cycles: Under 100,000

Description: Low production mold. Used only for limited production preferably with non-abrasive materials. Low to moderate price range.

Mold design recommended.

Mold base can be of mild steel or aluminum.

Cavities can be of aluminum, mild steel or any other agreed upon metal.

 

CLASS 105 MOLD

 

Cycles: Not exceeding 500

Description: Prototype only. This mold will be constructed in the least expensive manner possible to produce a very limited quantity of prototype parts.

May be constructed from cast metal or epoxy or any other material offering sufficient strength to produce minimum prototype pieces.

Mold Design Checklist

 

The following is a good checklist for reviewing Mold Drawings

Preliminary Drawing Checklist Items:

General layout

“A” side plan

“B” side plan

Front Section

Side Section

Title block is completely filled out on all drawings

Abbreviated BOM with ordering information for the Mold Base and primary Steels

Cavity Location

Parting line locations (Acceptable to customer)

Ejector Pin Layout (Acceptable to customer)

Waterline Layout

Balanced Runner layout

Gate type, and size specified

Side Action types & locations are shown

Concept of Tool operation

“O”  & “R” Dimensions noted

Note “Top of mold” & “Operator Side”

Will the tool fit in the correct press size

Knock out Locations

Support pillar layout

*  Typically, approval of the Preliminary designs approves our design concept.  Customer approval means that we can proceed with the Final Designs, that we can order the necessary materials, and that we can begin rough machining of material.  Sometimes, especially on “rush” jobs, customers approve finish machining based on the preliminary design.

Final Drawing Checklist Items:

All Preliminary Mold Drawings Requirements completed

Full Bill of Materials, Base Information, stamping notes, ejector information, special notes

Detailed views of every non-standard component.

Enough views, sections, iso views exist to adequately show part detail

All details are labeled with the detail number, name, material type, number required, Hardness, and surface finish.

Check All water lines for interference, including clearance for jiffy-plugs

Check Guide Pin length and clearance

Spring loads calculated & checked

Drawings appear to be adequately dimensioned

Critical Dimensions are noted

All “fit” areas are specified for each insert, side action, and core.

All draft is specified for cavity area, core pins, ribs, etc.

Check all side action angles and travel

Check for bad steel conditions (sharp edges, thin sections, too little shutoff, too little angle)

A & B Plan assembly views have been compared

All details from the assembly and plan views have been compared to the detail sheets.

All surface finishes are specified

Drawings are checked to the “Mold Info Sheet”.

*  Typically, by approving the Final designs the customer certifies that the drawings are dimensionally accurate, that critical areas have been noted, and that we can proceed with final machining, fit, and finishing.

Injection Molder and Molding Machines

Injection molder or injection molding machine is a machine for producing plastic molded parts by molding process. It has 2 main parts, an injection unit and a clamping unit.

An injection molder have 2 methods of fastening the mold -horizontal or vertical. Most injection molder are horizontally oriented because molded parts can easily be removed after ejection by leveraging gravity -the molded parts will just fall down into the container below. Vertical injection molders are used for insert molding applications because inserts are inserted into the core side of the mold before molding.

There are also manual injection molder for hobbyists. It is simple in consruction and does require manual force to inject the resin. An example of such machine is from Galomb, Inc. They make Benchtop injection molder.

Types of injection molding machines

Injection machines are classified mainly by the type of system that drives them: Hydraulic, electric, or hybrid.

Hydraulic injection machines uses ram system for its clamping mechanism. This type of machine is used by majority of molding companies.

Electric injection machines are driven by motors. Unlike the hydraulic machines, which continously pump hydraulics to the cylinder throughout the whole molding cycle, an electric machine only makes use of energy during closing and openning of the clamping unit. It uses toggle system for its clamping mechanism in order to build up tonnage. It is also faster, quieter, and have higher accuracy, but it is also known to be more expensive. The first maker of electric injection machine is Nissei Plastic Industrial Co., LTD.

 

 

Cordially

 

Amelia
B2B Marketing and Social Networking
CN Mould & Plastic Limited  (Video: http://www.youtube.com/watch?v=u2lgkSbNNkg )
Add: CN Hi-Tech industry park, No.227, Xiangshan Rd., Luotian 3rd industry zone, Songgang, Baoan, Shenzhen, 518105, China.
Tel: 86-755-86060383, 86061383, 86060363  Ext:828
Fax: 86-755-86060393
Skype: niya2000007
MSN : cntsales@live.cn
Email: sales@cnmouldplas.com
Website: www.cnmouldplas.com