Plastic Injection Molding

1

Plastic Injection Molding

Workplace Safety

By Clinton Cowen, President, CPC Plastics, Inc.

Table of Contents

I. Introduction

About the Author

About the Plastics Industry

Industry Safety Statistics

Industry Standards and Practices

II. Equipment and Environmental Considerations

Plant Design and Layout

Injection Molding Machinery

Peripheral Equipment

Assembly and Automation

Decoration and Packaging

Housekeeping

III. Industry Standards Enforcement

Common Industry Practices

Litigation and Compensation

IV. Industry Perception and Awareness

Who’s responsible?

Employers and Employees

Injection Molding Machinery Manufacturers

Safety Training and Awareness

Workforce Development

I. Introduction

About the Author

Clinton Cowen began working in plastic injection molding in 1991 after serving in the U.S. Navy as an avionics engineer. Mr. Cowen’s plastics career began as an electronics technician, responsible for the electronic, hydraulic, pneumatic and programming systems of injection molding machinery for one of the largest proprietary plastic container manufacturers in the US.

Through experience, education and training[1], Mr. Cowen advanced his troubleshooting skills at various leading proprietary and captive molders, before moving into the technical service field for global injection molding machinery manufacturing companies.

With this highly technical understanding of injection molding systems combined with the broad based industry experience Mr. Cowen founded CPC, Inc.[2], a plastic manufacturing company, base in Rhode Island, in 1998.

About the Plastics Industry

The plastic injection molding industry was born in Germany, 1921[3] with the invention of the first plastic injection molding machine. In 1932, the world’s first automatic injection molding machine would allow companies to mass manufacture their products in record time, thus the injection molder was born.

In its simplest form the plastics industry can be divided into two (2) sectors, these are referred to proprietary and custom or captive injection molder.

The proprietary molder customarily designs and manufactures the “core” plastic product(s) or components in house.

The custom molder generally takes on the responsibility of molding the part to the customers documented specifications, and in certain circumstances may aid in material selection and tooling design.

Since 1976[4], plastics have been the most widely used material in the United States. The ever growing demand for injection molded products, lends itself well to theentrepreneurial spirit. Colossal industries have been built and generations have been fed but is has not been without cost.

Industry Safety Statistics

In 2001, the plastics injection molding industry in the U.S. alone suffered twelve (12) fatalities and experienced an injury rate of 8.0 (N/EH x 200,000)[5]. One half (50%) of those fatalities were caused by “contact with objects or equipment”[6].

Fines levied by OSHA on plastics manufacturing companies for noncompliance during the period of October 2001 through September 2002 totaled over $1,000,000.00 USD[7].

The ten (10) most frequently cited standards for plastic injection molders during the period of October 2001 through September 2002[8] were:

1910.147The control of hazardous energy (lockout/tagout)

1910.212General requirements for all machines

1910.1200Hazard Communication

1910.305Electrical, Wiring Methods, Components and Equipment

1910.134Respiratory Protection.

1910.178Powered Industrial Trucks

1910.303Electrical Systems Design, General Requirements

1910.219Mechanical Power-Transmission Apparatus

1910.215Abrasive Wheel Machinery

1910.95Occupational Noise Exposure

The financial penalties imposed for each of the above infractions, during the same time period has been depicted in the chart below:

Industry Standards and Practices

Plastic injection molding safety standards are defined and enforced by the Occupational Safety and Health Administration, herein OSHA ( the American National Standards Institute, herein ANSI ( and approved State Occupational Safety and Health Plans, such as Michigan’s OSHP.

Plastic manufacturing employers must conform to OSHA’s general industry standard 29 CFR 1919[9], which applies to the major percentage of plastics processors operating under SIC code 3089.[10]

ANSI, a private non-profit organization (501(c)3) administers and coordinates the U.S. voluntary standardization and conformity assessment system[11]. As with most industries, organizations such as ANSI have developed standards primarily through relationships with the injection molding machinery manufacturers. Some of the current applicable ANSI standards are listed below:

ANSI/SPI B151.1-1997 (19.197).Applies to horizontal injection molding machines that are used in the rubber and plastics industries. Safety requirements of ancillary equipment used with horizontal injection molding machines are not covered by this standard.

• Summary of Interpretations of ANSI B151.1-1997. Machinery Division, the Society of the Plastics Industry, Inc. (

ANSI/SPI B151.27-1994 (1994) -Definitions and requirements for robots used with horizontal injection molding machines.

ANSI/SPI B151.29-2002 (2002) - Identifies and addresses known hazards to personnel working on or with the specified machinery.

ANSI/SPI B151.26-1993 - Dynamic Reaction Injection Molding Machines - Safety Requirements for the Manufacture, Care, and Use.

Other Standards, though not enforceable in the United States, contains information that may aid industry members in providing a safer and healthier workplace, such as the European ANSI equivalent:

European Standard EN 201:1997 - European Committee for Standardization (1997). (

II. Equipment and Environmental Considerations

Plant Design and Layout

Plant design and the layout of a plastic injection molding facility have the potential of effecting safety in a positive or negative way. Although many manufactures do not have the luxury of building a plant from the ground up, plastic injection molders can, through layout design, efficiently utilize their work space in a more ergonomic and safer way.

For example, a properly maintained central material handling system could drastically reduce the instances of “slip and fall” injuries, largely due to pelletized resin that has fallen onto to walkway surface.

For most custom or captive injection molders, a central material handling system is not realistic or cost effective, primarily because of the wide assortment of materials they manufacture. However, with some creative design, using existing technology, custom material systems that can prove agile enough for the custom molder, have the potential to reduce costs and instances of “slip and fall” injuries.

Additionally, segmenting “service centers” within a plastic manufacturing facility, such as an isolated mold repair workshop or automated assembly area, limits the primary exposure to only those employees who work in that area, and limited exposure means decreased risk.

Injection Molding Machinery

There are essentially two (2) types of injection molding machines, or IMM as it is often referred, horizontal and vertical with various clamp and injection unit(s) configurations. Some of these configurations can be seen below:

IMM configured for two color or multi-component molding are equipped with two (2) injection units and these can be mounted vertical, horizontal or combinations thereof.

Insert work and over-molding plastic manufactures tend to use a vertical clamp with a horizontal injection unit or “L” configuration as it is often referred.

In simple terms, the injection molding machine is comprised of two (2) primary components, the clamp, which when sized properly, supplies enough opposing force onto the tool (mold or die) to counteract pressure of the plastic melt being forced into it by the components, which make up the injection unit.

The clamp unit is constructed with, or a combination of, hydraulic, hydro-mechanical, electric or servo-electric clamping devices, while the injection unit is powered either hydraulically, electrically or a combination thereof.

The power plants (drive units) systems used in IMM vary by manufacturer and model. Most are equipped with a hydraulic, electric, and in some custom miniature IMM’s, pneumatic energy source(s) or a combination thereof.

Peripheral Equipment

A variety of peripheral and support equipment can be found on the plant floor at any given time. Below, I have outlined the most common peripheral or support equipment that one could find in an injection molding facility.

Tooling (molds or dies) found in the injection molding facilities typically use chilled or heated water (Thermalators) or hot oil units to allow the plastic to cure at a faster rate. These units can be a triple threat, slipping injuries caused by leaking water, burning caused by leaking hot water and trips caused by yards of hoses running to and from the unit and the mold.

Material granulators (grinders) are also highly used in the plastic injection molding industry. Defective product, runners, purging and other plastic scrap are reground in these machines, typically equipped with three (3) to four (4) rotating cutting blades, forcing the plastic between two (2) stationary (bed) knifes and shear the plastic into a size capable of being processed again and again. Plastic material that has been fed through a granulator is referred to as “regrind”.

Material dryers and blenders are used to prepare the plastic resin for molding. The material dryer (desiccant or dehumidifying) extracts the moisture from hydroscopic plastic resin until the desired dew point of the material has been reached.

Plastic parts that have not reached their ideal dew point or dried improperly can exhibit both visual and functional defects. Thus, it is a very important piece of equipment used in the plastics manufacturing process.

Assembly and Automation

Robotics and automation cells, such as the ones can be found in a large portion of captive or proprietary molding shops automate and accelerate the production process. These systems tend to be very unique and can prove to be quite a challenging when trying to develop a comprehensive safety guard (device).

Generally, automation and or robotic equipment, with proper function and design, have systems in place to protect the operator from being mauled by fast moving robotics or cylinders or amputated from unsuspecting pinch point.

Protective devices such as plastic safety guards equipped with electrical, mechanical, hydraulic or light barriers, which disconnect or in some case discharge the energy sources intended in the design.

Safety circuits found on robotics and automations cells can be comprised of one or all of the barriers mentioned above. Machinery and automation suppliers routinely use and collaborate to develop, redundant and or combinative systems in an effort to meet their industry’s standards and safety requirements.

Often, robotics and or the automation machinery are supplied by the IMM supplier that offers the optional robotic equipment on their injection molding machinery, coupled with custom automation cells per the client’s application.

This type of IMM and robotic and or automation configuration, when properly designed and functioning correctly, offers a more robust safety systems due to integration of the IMM and robot or automation.

Decoration and Packaging

In an effort to bring in additional sources of income and add value to their product or service(s), some plastic injection molders will offer hot stamping, pad printing, in-mold decoration or other decorative services.

The hot stamp machine uses a heated die, which strikes the plastic through a thin layer of foil or film and thermally transfers the image to the plastic part. This machinery most often uses a pneumatic, electric or hydraulic power plant and is basically comprised of a base and a head. The base holds the part in place, typically with a fixture, while the head is forced in a downward direction until striking the part.

III. Industry Standards and Enforcement

Regulatory Agencies

In the United States, OSHA is tasked the responsibility of enforcing federal, and in some cases state, violations of the general and industry standards that pertain to that particular industry. For the topic of this discussion, we will be discussing the enforcement of the plastic injection molding industry only.

OSHA conducted 58,402 state inspections in 2002[12]. Of those, approximately sixty-two (62%) percent were considered “High Hazard Targets”. Twenty-five (25%) were complaint or accident related and the remaining fourteen (14%) percent were from referrals or follow-up visits.

While OSHA has developed its own industry standards (General and Specific), plastics manufacturers must comply with the standards developed by ANSI (Industry Standards) and approved or common industry standards or practices.

The ANSI equivalent in Europe is the European Committee for Standardization or CEN as they are referred. As with their U.S. counterparts, CEN determines the standards for the plastic injection molding industry in Europe.

Common Industry Practices

Proprietary molders tend to be more automated in regards to material handling, robotics, automation and packaging. This is due in a large part because this kind of molder tends to make only one or a family of similar products.

Custom or captive molders on the other hand, tend be much less automated. Material is bought and stored in 50 lbs. bags or 1100 lbs. Gaylord boxes versus the silo’s that most proprietary molders maintain. This is due to the various plastic products that a custom molder may manufacture.

Instead of using central material loading systems like the proprietary molder, it is common for custom molders to hand load the hopper and or mixer unit of the IMM or use machine dedicated material loaders.

The process of moving either bags or Gaylord boxes in and out of the manufacturing floor increases the risk of pelletized resin falling onto the floor surfaces and thus increasing the potential for slip and fall injuries.

Another common practice in injection molding is referred to as purging or injecting plastic into the air so that any degraded (over heated or otherwise bad) material will be purged from the barrel unit. Although it may sound innocent, purging is the number one cause of burn injuries in the plastics injection molding industry.

This type of injury is commonly caused when the operator is hit with molten gaseous plastic resin that has been overheated in the barrel. As the plastic starts to degrade, gas begins to form under pressure do to either a material obstruction or in some cases, a hydraulically actuated shutoff nozzle, which intentionally blocks the flow of plastic.

The result of either is the same, material gases keep building and building until the unsuspecting operator begins to purge the machine, by the time that the operator realizes the dangerous situation, it’s too late.

Engineered resins such as Acetyl and POM rapid degrade and are highly volatile at elevated temperatures. The pressure that builds up can be quite high. I have witnessed metal hoppers filled with thirty (30) plus pounds of resin blow off the machine and land five (5) to ten (10) feet away.

In addition to purging the barrel, operators can experience similar conditions while cleaning or removing solid plastic material from the gate, the area were plastic enters the part, of a mold. This practice of “cleaning the gate” is necessary to allow hot molten plastic through the gate and into the mold.

Cleaning the tool at regular intervals is a common practice in the plastics injection molding industry. Depending on the level of service that the tool requires, it may be pulled from the machine and taken to a mold repair area or the work may be preformed in the machine.

The practice of maintaining a mold while it is mounted onto the machine, while not uncommon, can be quite dangerous if adequate safety standards are not met. Occasionally, overzealous, untrained or confused operators will make the mistake of reaching into the IMM while it is running in semi or automatic mode.

In fact, this action of leaning, reaching or entering into the molding area of the IMM while it is running is the leading cause of death in the injection molding industry. Additionally, these fatalities occur while mold or machine maintenance is being performed or when an operator reaches into the machine to remove a plastic part from the mold.

Often times, an unfamiliar or complacent eye will believe that the machine is in a rest or off (zero potential) position, when most likely it only paused briefly until the IMM receives an input via a machine operator or IMM, robotic or peripheral control circuitry.

Litigation and Compensation

Litigation involving plastic injection molding workplace injuries typically involves the injection molding machine (IMM) manufacturer,[13] the owner and or operator of the IMM,[14] the individual or company who sold the IMM and or any companies or individuals who have provided applicable maintenance or repair services on the IMM[15].

Complaints filed against the injection molding machinery suppliers, such as Ortiz v. HPM, Corp.[16], the claimant, Mr. Ortiz, argued that his injuries were the result of negligence, breach of express and implied warranty and strict liability, on the part of HPM Corporation, a named defendant. The California Court of Appeals (Second Appellate District Four) agreed, resulting in a $ 150,000.00 USD verdict in favor of Mr. Ortiz.

As in the above mentioned case, suits brought against the seller of an injection molding machine involving injury typically argues that a seller of used goods who makes extensive modifications to a product prior to the sale should be considered "tantamount to a manufacturer" and subject to strict liability.

It is important to note, plastic injection molders who sell their used equipment to other companies are named defendants in a substantial number of cases, where modifications are believed to have been made after the purchase, while in their custody or control, as in the case of Luke Allan Lund v. Pan American Machine Sales, LLC.[17]

Mr. Lund’s complaint argues that the machine was in an unsafe condition at the time of sale to his employer and that seller knew or should have known of the defective safety device while in its possession. Parties that engage in the selling of injection molding machinery either directly or indirectly, which involve injury, are finding themselves involved in litigation.

Consider Juana Balido v. Improved Machinery, Inc.[18], complainants charged negligence, breach of warranty, and strict liability after Balido's right hand was crushed when a plastic injection molding press closed as she was adjusting an insert. The Superior Court of Los Angeles County and the Court of Appeal of California upheld the decision handed out by the lower court, relieving the seller of liable, partly based upon disclosure of modifications and safety concerns prior to the sale.